diff --git a/src/components/structures/LeftPanel.tsx b/src/components/structures/LeftPanel.tsx
index 564484090a..2ea8920a19 100644
--- a/src/components/structures/LeftPanel.tsx
+++ b/src/components/structures/LeftPanel.tsx
@@ -68,7 +68,7 @@ interface IState {
 export default class LeftPanel extends React.Component<IProps, IState> {
     private listContainerRef = createRef<HTMLDivElement>();
     private roomListRef = createRef<RoomList>();
-    private focusedElement: Element = null;
+    private focusedElement: Element | null = null;
     private isDoingStickyHeaders = false;
 
     public constructor(props: IProps) {
diff --git a/src/components/views/dialogs/security/AccessSecretStorageDialog.tsx b/src/components/views/dialogs/security/AccessSecretStorageDialog.tsx
index 4873173a3e..0cf19b4eb2 100644
--- a/src/components/views/dialogs/security/AccessSecretStorageDialog.tsx
+++ b/src/components/views/dialogs/security/AccessSecretStorageDialog.tsx
@@ -41,7 +41,7 @@ const KEY_FILE_MAX_SIZE = 128;
 const VALIDATION_THROTTLE_MS = 200;
 
 interface IProps extends IDialogProps {
-    keyInfo: ISecretStorageKeyInfo;
+    keyInfo?: ISecretStorageKeyInfo;
     checkPrivateKey: (k: { passphrase?: string; recoveryKey?: string }) => boolean;
 }
 
@@ -137,7 +137,7 @@ export default class AccessSecretStorageDialog extends React.PureComponent<IProp
     };
 
     private onRecoveryKeyFileChange = async (ev: ChangeEvent<HTMLInputElement>): Promise<void> => {
-        if (ev.target.files.length === 0) return;
+        if (!ev.target.files?.length) return;
 
         const f = ev.target.files[0];
 
@@ -170,7 +170,7 @@ export default class AccessSecretStorageDialog extends React.PureComponent<IProp
     };
 
     private onRecoveryKeyFileUploadClick = (): void => {
-        this.fileUpload.current.click();
+        this.fileUpload.current?.click();
     };
 
     private onPassPhraseNext = async (ev: FormEvent<HTMLFormElement> | React.MouseEvent): Promise<void> => {
@@ -269,15 +269,11 @@ export default class AccessSecretStorageDialog extends React.PureComponent<IProp
     }
 
     public render(): React.ReactNode {
-        const hasPassphrase =
-            this.props.keyInfo &&
-            this.props.keyInfo.passphrase &&
-            this.props.keyInfo.passphrase.salt &&
-            this.props.keyInfo.passphrase.iterations;
+        const hasPassphrase = this.props.keyInfo?.passphrase?.salt && this.props.keyInfo?.passphrase?.iterations;
 
         const resetButton = (
             <div className="mx_AccessSecretStorageDialog_reset">
-                {_t("Forgotten or lost all recovery methods? <a>Reset all</a>", null, {
+                {_t("Forgotten or lost all recovery methods? <a>Reset all</a>", undefined, {
                     a: (sub) => (
                         <AccessibleButton
                             kind="link_inline"
@@ -405,7 +401,7 @@ export default class AccessSecretStorageDialog extends React.PureComponent<IProp
                                     value={this.state.recoveryKey}
                                     onChange={this.onRecoveryKeyChange}
                                     autoFocus={true}
-                                    forceValidity={this.state.recoveryKeyCorrect}
+                                    forceValidity={this.state.recoveryKeyCorrect ?? undefined}
                                     autoComplete="off"
                                 />
                             </div>
diff --git a/src/components/views/elements/Field.tsx b/src/components/views/elements/Field.tsx
index 1afe52810b..bcf8b00d4f 100644
--- a/src/components/views/elements/Field.tsx
+++ b/src/components/views/elements/Field.tsx
@@ -112,8 +112,8 @@ export interface INativeOnChangeInputProps extends IProps, InputHTMLAttributes<H
 type PropShapes = IInputProps | ISelectProps | ITextareaProps | INativeOnChangeInputProps;
 
 interface IState {
-    valid: boolean;
-    feedback: React.ReactNode;
+    valid?: boolean;
+    feedback?: React.ReactNode;
     feedbackVisible: boolean;
     focused: boolean;
 }
@@ -148,8 +148,6 @@ export default class Field extends React.PureComponent<PropShapes, IState> {
     public constructor(props: PropShapes) {
         super(props);
         this.state = {
-            valid: undefined,
-            feedback: undefined,
             feedbackVisible: false,
             focused: false,
         };
@@ -199,7 +197,7 @@ export default class Field extends React.PureComponent<PropShapes, IState> {
         this.props.onBlur?.(ev);
     };
 
-    public async validate({ focused, allowEmpty = true }: IValidateOpts): Promise<boolean> {
+    public async validate({ focused, allowEmpty = true }: IValidateOpts): Promise<boolean | undefined> {
         if (!this.props.onValidate) {
             return;
         }
@@ -268,11 +266,11 @@ export default class Field extends React.PureComponent<PropShapes, IState> {
 
         const fieldInput = React.createElement(this.props.element, inputProps_, children);
 
-        let prefixContainer = null;
+        let prefixContainer: JSX.Element | undefined;
         if (prefixComponent) {
             prefixContainer = <span className="mx_Field_prefix">{prefixComponent}</span>;
         }
-        let postfixContainer = null;
+        let postfixContainer: JSX.Element | undefined;
         if (postfixComponent) {
             postfixContainer = <span className="mx_Field_postfix">{postfixComponent}</span>;
         }
diff --git a/src/components/views/room_settings/UrlPreviewSettings.tsx b/src/components/views/room_settings/UrlPreviewSettings.tsx
index d24d878b40..ead58aa328 100644
--- a/src/components/views/room_settings/UrlPreviewSettings.tsx
+++ b/src/components/views/room_settings/UrlPreviewSettings.tsx
@@ -17,7 +17,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { Room } from "matrix-js-sdk/src/models/room";
 
 import { _t, _td } from "../../../languageHandler";
@@ -41,12 +41,12 @@ export default class UrlPreviewSettings extends React.Component<IProps> {
         dis.fire(Action.ViewUserSettings);
     };
 
-    public render(): React.ReactNode {
+    public render(): ReactNode {
         const roomId = this.props.room.roomId;
         const isEncrypted = MatrixClientPeg.get().isRoomEncrypted(roomId);
 
-        let previewsForAccount = null;
-        let previewsForRoom = null;
+        let previewsForAccount: ReactNode | undefined;
+        let previewsForRoom: ReactNode | undefined;
 
         if (!isEncrypted) {
             // Only show account setting state and room state setting state in non-e2ee rooms where they apply
diff --git a/src/components/views/settings/LayoutSwitcher.tsx b/src/components/views/settings/LayoutSwitcher.tsx
index 3e265857fc..462147df2e 100644
--- a/src/components/views/settings/LayoutSwitcher.tsx
+++ b/src/components/views/settings/LayoutSwitcher.tsx
@@ -28,10 +28,10 @@ import { SettingLevel } from "../../../settings/SettingLevel";
 
 interface IProps {
     userId?: string;
-    displayName: string;
-    avatarUrl: string;
+    displayName?: string;
+    avatarUrl?: string;
     messagePreviewText: string;
-    onLayoutChanged?: (layout: Layout) => void;
+    onLayoutChanged: (layout: Layout) => void;
 }
 
 interface IState {
diff --git a/src/components/views/settings/Notifications.tsx b/src/components/views/settings/Notifications.tsx
index 2278425db8..b4ed0c680f 100644
--- a/src/components/views/settings/Notifications.tsx
+++ b/src/components/views/settings/Notifications.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { IAnnotatedPushRule, IPusher, PushRuleAction, PushRuleKind, RuleId } from "matrix-js-sdk/src/@types/PushRules";
 import { IThreepid, ThreepidMedium } from "matrix-js-sdk/src/@types/threepids";
 import { logger } from "matrix-js-sdk/src/logger";
@@ -152,7 +152,7 @@ export default class Notifications extends React.PureComponent<IProps, IState> {
         // the master rule is *enabled* it means all other rules are *disabled* (or
         // inhibited). Conversely, when the master rule is *disabled* then all other rules
         // are *enabled* (or operate fine).
-        return this.state.masterPushRule?.enabled;
+        return !!this.state.masterPushRule?.enabled;
     }
 
     public componentDidMount(): void {
@@ -622,12 +622,12 @@ export default class Notifications extends React.PureComponent<IProps, IState> {
         );
     }
 
-    private renderCategory(category: RuleClass): JSX.Element {
+    private renderCategory(category: RuleClass): ReactNode {
         if (category !== RuleClass.VectorOther && this.isInhibited) {
             return null; // nothing to show for the section
         }
 
-        let clearNotifsButton: JSX.Element;
+        let clearNotifsButton: JSX.Element | undefined;
         if (
             category === RuleClass.VectorOther &&
             MatrixClientPeg.get()
@@ -660,7 +660,7 @@ export default class Notifications extends React.PureComponent<IProps, IState> {
             return null;
         }
 
-        let keywordComposer: JSX.Element;
+        let keywordComposer: JSX.Element | undefined;
         if (category === RuleClass.VectorMentions) {
             keywordComposer = (
                 <TagComposer
@@ -691,7 +691,7 @@ export default class Notifications extends React.PureComponent<IProps, IState> {
             />
         );
 
-        const fieldsetRows = this.state.vectorPushRules[category].map((r) => (
+        const fieldsetRows = this.state.vectorPushRules[category]?.map((r) => (
             <fieldset
                 key={category + r.ruleId}
                 data-testid={category + r.ruleId}
@@ -736,10 +736,10 @@ export default class Notifications extends React.PureComponent<IProps, IState> {
         );
     }
 
-    private renderTargets(): JSX.Element {
+    private renderTargets(): ReactNode {
         if (this.isInhibited) return null; // no targets if there's no notifications
 
-        const rows = this.state.pushers.map((p) => (
+        const rows = this.state.pushers?.map((p) => (
             <tr key={p.kind + p.pushkey}>
                 <td>{p.app_display_name}</td>
                 <td>{p.device_display_name}</td>
diff --git a/src/components/views/settings/ProfileSettings.tsx b/src/components/views/settings/ProfileSettings.tsx
index 0a7bd4a042..5bba1c51b3 100644
--- a/src/components/views/settings/ProfileSettings.tsx
+++ b/src/components/views/settings/ProfileSettings.tsx
@@ -34,11 +34,11 @@ import PosthogTrackers from "../../../PosthogTrackers";
 
 interface IState {
     userId?: string;
-    originalDisplayName?: string;
-    displayName?: string;
-    originalAvatarUrl?: string;
+    originalDisplayName: string;
+    displayName: string;
+    originalAvatarUrl: string | null;
     avatarUrl?: string | ArrayBuffer;
-    avatarFile?: File;
+    avatarFile?: File | null;
     enableProfileSave?: boolean;
 }
 
@@ -52,25 +52,25 @@ export default class ProfileSettings extends React.Component<{}, IState> {
         let avatarUrl = OwnProfileStore.instance.avatarMxc;
         if (avatarUrl) avatarUrl = mediaFromMxc(avatarUrl).getSquareThumbnailHttp(96);
         this.state = {
-            userId: client.getUserId(),
-            originalDisplayName: OwnProfileStore.instance.displayName,
-            displayName: OwnProfileStore.instance.displayName,
+            userId: client.getUserId()!,
+            originalDisplayName: OwnProfileStore.instance.displayName ?? "",
+            displayName: OwnProfileStore.instance.displayName ?? "",
             originalAvatarUrl: avatarUrl,
-            avatarUrl: avatarUrl,
+            avatarUrl: avatarUrl ?? undefined,
             avatarFile: null,
             enableProfileSave: false,
         };
     }
 
     private uploadAvatar = (): void => {
-        this.avatarUpload.current.click();
+        this.avatarUpload.current?.click();
     };
 
     private removeAvatar = (): void => {
         // clear file upload field so same file can be selected
         this.avatarUpload.current.value = "";
         this.setState({
-            avatarUrl: null,
+            avatarUrl: undefined,
             avatarFile: null,
             enableProfileSave: true,
         });
@@ -84,7 +84,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
         this.setState({
             enableProfileSave: false,
             displayName: this.state.originalDisplayName,
-            avatarUrl: this.state.originalAvatarUrl,
+            avatarUrl: this.state.originalAvatarUrl ?? undefined,
             avatarFile: null,
         });
     };
@@ -97,7 +97,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
         this.setState({ enableProfileSave: false });
 
         const client = MatrixClientPeg.get();
-        const newState: IState = {};
+        const newState: Partial<IState> = {};
 
         const displayName = this.state.displayName.trim();
         try {
@@ -114,7 +114,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
                 );
                 const { content_uri: uri } = await client.uploadContent(this.state.avatarFile);
                 await client.setAvatarUrl(uri);
-                newState.avatarUrl = mediaFromMxc(uri).getSquareThumbnailHttp(96);
+                newState.avatarUrl = mediaFromMxc(uri).getSquareThumbnailHttp(96) ?? undefined;
                 newState.originalAvatarUrl = newState.avatarUrl;
                 newState.avatarFile = null;
             } else if (this.state.originalAvatarUrl !== this.state.avatarUrl) {
@@ -128,7 +128,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
             });
         }
 
-        this.setState(newState);
+        this.setState<any>(newState);
     };
 
     private onDisplayNameChanged = (e: React.ChangeEvent<HTMLInputElement>): void => {
@@ -141,7 +141,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
     private onAvatarChanged = (e: React.ChangeEvent<HTMLInputElement>): void => {
         if (!e.target.files || !e.target.files.length) {
             this.setState({
-                avatarUrl: this.state.originalAvatarUrl,
+                avatarUrl: this.state.originalAvatarUrl ?? undefined,
                 avatarFile: null,
                 enableProfileSave: false,
             });
@@ -152,7 +152,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
         const reader = new FileReader();
         reader.onload = (ev) => {
             this.setState({
-                avatarUrl: ev.target.result,
+                avatarUrl: ev.target?.result,
                 avatarFile: file,
                 enableProfileSave: true,
             });
@@ -162,7 +162,7 @@ export default class ProfileSettings extends React.Component<{}, IState> {
 
     public render(): React.ReactNode {
         const hostingSignupLink = getHostingLink("user-settings");
-        let hostingSignup = null;
+        let hostingSignup: JSX.Element | undefined;
         if (hostingSignupLink) {
             hostingSignup = (
                 <span>
diff --git a/src/components/views/settings/SetIntegrationManager.tsx b/src/components/views/settings/SetIntegrationManager.tsx
index 4013ed4c40..0290c4b7fe 100644
--- a/src/components/views/settings/SetIntegrationManager.tsx
+++ b/src/components/views/settings/SetIntegrationManager.tsx
@@ -27,7 +27,7 @@ import ToggleSwitch from "../elements/ToggleSwitch";
 interface IProps {}
 
 interface IState {
-    currentManager: IntegrationManagerInstance;
+    currentManager: IntegrationManagerInstance | null;
     provisioningEnabled: boolean;
 }
 
diff --git a/src/components/views/settings/ThemeChoicePanel.tsx b/src/components/views/settings/ThemeChoicePanel.tsx
index afbe555137..df769a9456 100644
--- a/src/components/views/settings/ThemeChoicePanel.tsx
+++ b/src/components/views/settings/ThemeChoicePanel.tsx
@@ -162,7 +162,7 @@ export default class ThemeChoicePanel extends React.Component<IProps, IState> {
         this.setState({ customThemeUrl: e.target.value });
     };
 
-    private renderHighContrastCheckbox(): React.ReactElement<HTMLDivElement> {
+    private renderHighContrastCheckbox(): React.ReactElement<HTMLDivElement> | undefined {
         if (
             !this.state.useSystemTheme &&
             (findHighContrastTheme(this.state.theme) || isHighContrastTheme(this.state.theme))
@@ -181,7 +181,7 @@ export default class ThemeChoicePanel extends React.Component<IProps, IState> {
     }
 
     private highContrastThemeChanged(checked: boolean): void {
-        let newTheme: string;
+        let newTheme: string | undefined;
         if (checked) {
             newTheme = findHighContrastTheme(this.state.theme);
         } else {
@@ -194,7 +194,7 @@ export default class ThemeChoicePanel extends React.Component<IProps, IState> {
 
     public render(): React.ReactElement<HTMLDivElement> {
         const themeWatcher = new ThemeWatcher();
-        let systemThemeSection: JSX.Element;
+        let systemThemeSection: JSX.Element | undefined;
         if (themeWatcher.isSystemThemeSupported()) {
             systemThemeSection = (
                 <div>
@@ -208,9 +208,9 @@ export default class ThemeChoicePanel extends React.Component<IProps, IState> {
             );
         }
 
-        let customThemeForm: JSX.Element;
+        let customThemeForm: JSX.Element | undefined;
         if (SettingsStore.getValue("feature_custom_themes")) {
-            let messageElement = null;
+            let messageElement: JSX.Element | undefined;
             if (this.state.customThemeMessage.text) {
                 if (this.state.customThemeMessage.isError) {
                     messageElement = <div className="text-error">{this.state.customThemeMessage.text}</div>;
@@ -268,7 +268,7 @@ export default class ThemeChoicePanel extends React.Component<IProps, IState> {
         );
     }
 
-    public apparentSelectedThemeId(): string {
+    public apparentSelectedThemeId(): string | undefined {
         if (this.state.useSystemTheme) {
             return undefined;
         }
diff --git a/src/components/views/settings/UpdateCheckButton.tsx b/src/components/views/settings/UpdateCheckButton.tsx
index a39ba102e5..da88106749 100644
--- a/src/components/views/settings/UpdateCheckButton.tsx
+++ b/src/components/views/settings/UpdateCheckButton.tsx
@@ -27,7 +27,7 @@ import AccessibleButton from "../../../components/views/elements/AccessibleButto
 import { CheckUpdatesPayload } from "../../../dispatcher/payloads/CheckUpdatesPayload";
 
 function installUpdate(): void {
-    PlatformPeg.get().installUpdate();
+    PlatformPeg.get()?.installUpdate();
 }
 
 function getStatusText(status: UpdateCheckStatus, errorDetail?: string): ReactNode {
@@ -58,11 +58,11 @@ function getStatusText(status: UpdateCheckStatus, errorDetail?: string): ReactNo
 const doneStatuses = [UpdateCheckStatus.Ready, UpdateCheckStatus.Error, UpdateCheckStatus.NotAvailable];
 
 const UpdateCheckButton: React.FC = () => {
-    const [state, setState] = useState<CheckUpdatesPayload>(null);
+    const [state, setState] = useState<CheckUpdatesPayload | null>(null);
 
     const onCheckForUpdateClick = (): void => {
         setState(null);
-        PlatformPeg.get().startUpdateCheck();
+        PlatformPeg.get()?.startUpdateCheck();
     };
 
     useDispatcher(dis, ({ action, ...params }) => {
@@ -71,9 +71,9 @@ const UpdateCheckButton: React.FC = () => {
         }
     });
 
-    const busy = state && !doneStatuses.includes(state.status);
+    const busy = !!state && !doneStatuses.includes(state.status);
 
-    let suffix;
+    let suffix: JSX.Element | undefined;
     if (state) {
         suffix = (
             <span className="mx_UpdateCheckButton_summary">
diff --git a/src/components/views/settings/devices/DeviceDetails.tsx b/src/components/views/settings/devices/DeviceDetails.tsx
index 1793fc8b5e..56df38c6cf 100644
--- a/src/components/views/settings/devices/DeviceDetails.tsx
+++ b/src/components/views/settings/devices/DeviceDetails.tsx
@@ -31,14 +31,14 @@ import { ExtendedDevice } from "./types";
 
 interface Props {
     device: ExtendedDevice;
-    pusher?: IPusher | undefined;
-    localNotificationSettings?: LocalNotificationSettings | undefined;
+    pusher?: IPusher;
+    localNotificationSettings?: LocalNotificationSettings;
     isSigningOut: boolean;
     onVerifyDevice?: () => void;
     onSignOutDevice: () => void;
     saveDeviceName: (deviceName: string) => Promise<void>;
-    setPushNotifications?: (deviceId: string, enabled: boolean) => Promise<void> | undefined;
-    supportsMSC3881?: boolean | undefined;
+    setPushNotifications?: (deviceId: string, enabled: boolean) => Promise<void>;
+    supportsMSC3881?: boolean;
     className?: string;
     isCurrentDevice?: boolean;
 }
diff --git a/src/components/views/settings/devices/LoginWithQRSection.tsx b/src/components/views/settings/devices/LoginWithQRSection.tsx
index 0faa3913c8..356084dec7 100644
--- a/src/components/views/settings/devices/LoginWithQRSection.tsx
+++ b/src/components/views/settings/devices/LoginWithQRSection.tsx
@@ -23,7 +23,7 @@ import SettingsSubsection from "../shared/SettingsSubsection";
 
 interface IProps {
     onShowQr: () => void;
-    versions: IServerVersions;
+    versions?: IServerVersions;
 }
 
 export default class LoginWithQRSection extends React.Component<IProps> {
diff --git a/src/components/views/settings/tabs/room/AdvancedRoomSettingsTab.tsx b/src/components/views/settings/tabs/room/AdvancedRoomSettingsTab.tsx
index 943634f873..34153819fc 100644
--- a/src/components/views/settings/tabs/room/AdvancedRoomSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/AdvancedRoomSettingsTab.tsx
@@ -40,6 +40,7 @@ interface IRecommendedVersion {
 }
 
 interface IState {
+    // This is eventually set to the value of room.getRecommendedVersion()
     upgradeRecommendation?: IRecommendedVersion;
     oldRoomId?: string;
     oldEventId?: string;
@@ -52,14 +53,11 @@ export default class AdvancedRoomSettingsTab extends React.Component<IProps, ISt
 
         const msc3946ProcessDynamicPredecessor = SettingsStore.getValue("feature_dynamic_room_predecessors");
 
-        this.state = {
-            // This is eventually set to the value of room.getRecommendedVersion()
-            upgradeRecommendation: null,
-        };
+        this.state = {};
 
         // we handle lack of this object gracefully later, so don't worry about it failing here.
         const room = MatrixClientPeg.get().getRoom(this.props.roomId);
-        room.getRecommendedVersion().then((v) => {
+        room?.getRecommendedVersion().then((v) => {
             const tombstone = room.currentState.getStateEvents(EventType.RoomTombstone, "");
 
             const additionalStateChanges: Partial<IState> = {};
@@ -99,11 +97,10 @@ export default class AdvancedRoomSettingsTab extends React.Component<IProps, ISt
     public render(): React.ReactNode {
         const client = MatrixClientPeg.get();
         const room = client.getRoom(this.props.roomId);
-        const isSpace = room.isSpaceRoom();
+        const isSpace = room?.isSpaceRoom();
 
-        let unfederatableSection;
-        const createEvent = room.currentState.getStateEvents(EventType.RoomCreate, "");
-        if (createEvent && createEvent.getContent()["m.federate"] === false) {
+        let unfederatableSection: JSX.Element | undefined;
+        if (room?.currentState.getStateEvents(EventType.RoomCreate, "")?.getContent()["m.federate"] === false) {
             unfederatableSection = <div>{_t("This room is not accessible by remote Matrix servers")}</div>;
         }
 
@@ -132,13 +129,13 @@ export default class AdvancedRoomSettingsTab extends React.Component<IProps, ISt
             );
         }
 
-        let oldRoomLink;
+        let oldRoomLink: JSX.Element | undefined;
         if (this.state.oldRoomId) {
             let copy: string;
             if (isSpace) {
-                copy = _t("View older version of %(spaceName)s.", { spaceName: room.name });
+                copy = _t("View older version of %(spaceName)s.", { spaceName: room?.name ?? this.state.oldRoomId });
             } else {
-                copy = _t("View older messages in %(roomName)s.", { roomName: room.name });
+                copy = _t("View older messages in %(roomName)s.", { roomName: room?.name ?? this.state.oldRoomId });
             }
 
             oldRoomLink = (
@@ -165,7 +162,7 @@ export default class AdvancedRoomSettingsTab extends React.Component<IProps, ISt
                     <span className="mx_SettingsTab_subheading">{_t("Room version")}</span>
                     <div>
                         <span>{_t("Room version:")}</span>&nbsp;
-                        {room.getVersion()}
+                        {room?.getVersion()}
                     </div>
                     {oldRoomLink}
                     {roomUpgradeButton}
diff --git a/src/components/views/settings/tabs/room/BridgeSettingsTab.tsx b/src/components/views/settings/tabs/room/BridgeSettingsTab.tsx
index d33ef0e880..4eb676f411 100644
--- a/src/components/views/settings/tabs/room/BridgeSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/BridgeSettingsTab.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { Room } from "matrix-js-sdk/src/models/room";
 import { MatrixEvent } from "matrix-js-sdk/src/models/event";
 
@@ -34,17 +34,16 @@ interface IProps {
 }
 
 export default class BridgeSettingsTab extends React.Component<IProps> {
-    private renderBridgeCard(event: MatrixEvent, room: Room): JSX.Element {
+    private renderBridgeCard(event: MatrixEvent, room: Room | null): ReactNode {
         const content = event.getContent();
-        if (!content || !content.channel || !content.protocol) {
-            return null;
-        }
+        if (!room || !content?.channel || !content.protocol) return null;
         return <BridgeTile key={event.getId()} room={room} ev={event} />;
     }
 
     public static getBridgeStateEvents(roomId: string): MatrixEvent[] {
         const client = MatrixClientPeg.get();
-        const roomState = client.getRoom(roomId).currentState;
+        const roomState = client.getRoom(roomId)?.currentState;
+        if (!roomState) return [];
 
         return BRIDGE_EVENT_TYPES.map((typeName) => roomState.getStateEvents(typeName)).flat(1);
     }
diff --git a/src/components/views/settings/tabs/room/GeneralRoomSettingsTab.tsx b/src/components/views/settings/tabs/room/GeneralRoomSettingsTab.tsx
index e154687759..9c47a7432e 100644
--- a/src/components/views/settings/tabs/room/GeneralRoomSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/GeneralRoomSettingsTab.tsx
@@ -61,15 +61,14 @@ export default class GeneralRoomSettingsTab extends React.Component<IProps, ISta
         const room = client.getRoom(this.props.roomId);
 
         const canSetAliases = true; // Previously, we arbitrarily only allowed admins to do this
-        const canSetCanonical = room.currentState.mayClientSendStateEvent("m.room.canonical_alias", client);
-        const canonicalAliasEv = room.currentState.getStateEvents("m.room.canonical_alias", "");
+        const canSetCanonical = room?.currentState.mayClientSendStateEvent("m.room.canonical_alias", client);
+        const canonicalAliasEv = room?.currentState.getStateEvents("m.room.canonical_alias", "") ?? undefined;
 
-        const urlPreviewSettings = SettingsStore.getValue(UIFeature.URLPreviews) ? (
-            <UrlPreviewSettings room={room} />
-        ) : null;
+        const urlPreviewSettings =
+            room && SettingsStore.getValue(UIFeature.URLPreviews) ? <UrlPreviewSettings room={room} /> : null;
 
         let leaveSection;
-        if (room.getMyMembership() === "join") {
+        if (room?.getMyMembership() === "join") {
             leaveSection = (
                 <>
                     <span className="mx_SettingsTab_subheading">{_t("Leave room")}</span>
diff --git a/src/components/views/settings/tabs/room/NotificationSettingsTab.tsx b/src/components/views/settings/tabs/room/NotificationSettingsTab.tsx
index e52967d086..b9c481125a 100644
--- a/src/components/views/settings/tabs/room/NotificationSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/NotificationSettingsTab.tsx
@@ -40,7 +40,7 @@ interface IProps {
 
 interface IState {
     currentSound: string;
-    uploadedFile: File;
+    uploadedFile: File | null;
 }
 
 export default class NotificationsSettingsTab extends React.Component<IProps, IState> {
@@ -71,7 +71,7 @@ export default class NotificationsSettingsTab extends React.Component<IProps, IS
         e.stopPropagation();
         e.preventDefault();
 
-        this.soundUpload.current.click();
+        this.soundUpload.current?.click();
     };
 
     private onSoundUploadChanged = (e: React.ChangeEvent<HTMLInputElement>): void => {
@@ -156,7 +156,7 @@ export default class NotificationsSettingsTab extends React.Component<IProps, IS
     };
 
     public render(): React.ReactNode {
-        let currentUploadedFile = null;
+        let currentUploadedFile: JSX.Element | undefined;
         if (this.state.uploadedFile) {
             currentUploadedFile = (
                 <div>
diff --git a/src/components/views/settings/tabs/room/RolesRoomSettingsTab.tsx b/src/components/views/settings/tabs/room/RolesRoomSettingsTab.tsx
index 6705b5ee2a..db39176257 100644
--- a/src/components/views/settings/tabs/room/RolesRoomSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/RolesRoomSettingsTab.tsx
@@ -239,13 +239,13 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
     public render(): React.ReactNode {
         const client = MatrixClientPeg.get();
         const room = client.getRoom(this.props.roomId);
-        const isSpaceRoom = room.isSpaceRoom();
+        const isSpaceRoom = room?.isSpaceRoom();
 
-        const plEvent = room.currentState.getStateEvents(EventType.RoomPowerLevels, "");
+        const plEvent = room?.currentState.getStateEvents(EventType.RoomPowerLevels, "");
         const plContent = plEvent ? plEvent.getContent() || {} : {};
-        const canChangeLevels = room.currentState.mayClientSendStateEvent(EventType.RoomPowerLevels, client);
+        const canChangeLevels = room?.currentState.mayClientSendStateEvent(EventType.RoomPowerLevels, client);
 
-        const plEventsToLabels: Record<EventType | string, string> = {
+        const plEventsToLabels: Record<EventType | string, string | null> = {
             // These will be translated for us later.
             [EventType.RoomAvatar]: isSpaceRoom ? _td("Change space avatar") : _td("Change room avatar"),
             [EventType.RoomName]: isSpaceRoom ? _td("Change space name") : _td("Change room name"),
@@ -322,7 +322,7 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
             powerLevelDescriptors.users_default.defaultValue,
         );
 
-        let currentUserLevel = userLevels[client.getUserId()];
+        let currentUserLevel = userLevels[client.getUserId()!];
         if (currentUserLevel === undefined) {
             currentUserLevel = defaultUserLevel;
         }
@@ -391,16 +391,16 @@ export default class RolesRoomSettingsTab extends React.Component<IProps> {
             }
         }
 
-        const banned = room.getMembersWithMembership("ban");
-        let bannedUsersSection;
-        if (banned.length) {
+        const banned = room?.getMembersWithMembership("ban");
+        let bannedUsersSection: JSX.Element | undefined;
+        if (banned?.length) {
             const canBanUsers = currentUserLevel >= banLevel;
             bannedUsersSection = (
                 <SettingsFieldset legend={_t("Banned users")}>
                     <ul>
                         {banned.map((member) => {
-                            const banEvent = member.events.member.getContent();
-                            const sender = room.getMember(member.events.member.getSender());
+                            const banEvent = member.events.member?.getContent();
+                            const sender = room?.getMember(member.events.member.getSender());
                             let bannedBy = member.events.member.getSender(); // start by falling back to mxid
                             if (sender) bannedBy = sender.name;
                             return (
diff --git a/src/components/views/settings/tabs/room/SecurityRoomSettingsTab.tsx b/src/components/views/settings/tabs/room/SecurityRoomSettingsTab.tsx
index 656d171638..4c8cc9d967 100644
--- a/src/components/views/settings/tabs/room/SecurityRoomSettingsTab.tsx
+++ b/src/components/views/settings/tabs/room/SecurityRoomSettingsTab.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { GuestAccess, HistoryVisibility, JoinRule } from "matrix-js-sdk/src/@types/partials";
 import { MatrixEvent } from "matrix-js-sdk/src/models/event";
 import { RoomStateEvent } from "matrix-js-sdk/src/models/room-state";
@@ -61,16 +61,16 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
     public constructor(props: IProps, context: React.ContextType<typeof MatrixClientContext>) {
         super(props, context);
 
-        const state = context.getRoom(this.props.roomId).currentState;
+        const state = context.getRoom(this.props.roomId)?.currentState;
 
         this.state = {
             guestAccess: this.pullContentPropertyFromEvent<GuestAccess>(
-                state.getStateEvents(EventType.RoomGuestAccess, ""),
+                state?.getStateEvents(EventType.RoomGuestAccess, ""),
                 "guest_access",
                 GuestAccess.Forbidden,
             ),
             history: this.pullContentPropertyFromEvent<HistoryVisibility>(
-                state.getStateEvents(EventType.RoomHistoryVisibility, ""),
+                state?.getStateEvents(EventType.RoomHistoryVisibility, ""),
                 "history_visibility",
                 HistoryVisibility.Shared,
             ),
@@ -85,7 +85,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
         this.hasAliases().then((hasAliases) => this.setState({ hasAliases }));
     }
 
-    private pullContentPropertyFromEvent<T>(event: MatrixEvent, key: string, defaultValue: T): T {
+    private pullContentPropertyFromEvent<T>(event: MatrixEvent | null | undefined, key: string, defaultValue: T): T {
         return event?.getContent()[key] || defaultValue;
     }
 
@@ -117,7 +117,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
                                     "You'll get none of the benefits of encryption, and you won't be able to turn it " +
                                     "off later. Encrypting messages in a public room will make receiving and sending " +
                                     "messages slower.",
-                                null,
+                                undefined,
                                 { b: (sub) => <b>{sub}</b> },
                             )}{" "}
                         </p>
@@ -126,7 +126,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
                             {_t(
                                 "To avoid these issues, create a <a>new encrypted room</a> for " +
                                     "the conversation you plan to have.",
-                                null,
+                                undefined,
                                 {
                                     a: (sub) => (
                                         <AccessibleButton
@@ -236,7 +236,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
     };
 
     private updateBlacklistDevicesFlag = (checked: boolean): void => {
-        this.context.getRoom(this.props.roomId).setBlacklistUnverifiedDevices(checked);
+        this.context.getRoom(this.props.roomId)?.setBlacklistUnverifiedDevices(checked);
     };
 
     private async hasAliases(): Promise<boolean> {
@@ -250,8 +250,8 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
         const client = this.context;
         const room = client.getRoom(this.props.roomId);
 
-        let aliasWarning = null;
-        if (room.getJoinRule() === JoinRule.Public && !this.state.hasAliases) {
+        let aliasWarning: JSX.Element | undefined;
+        if (room?.getJoinRule() === JoinRule.Public && !this.state.hasAliases) {
             aliasWarning = (
                 <div className="mx_SecurityRoomSettingsTab_warning">
                     <WarningIcon width={15} height={15} />
@@ -297,7 +297,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
                                     "It will mean anyone can find and join the room, so anyone can read messages. " +
                                     "You'll get none of the benefits of encryption. Encrypting messages in a public " +
                                     "room will make receiving and sending messages slower.",
-                                null,
+                                undefined,
                                 { b: (sub) => <b>{sub}</b> },
                             )}{" "}
                         </p>
@@ -306,7 +306,7 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
                             {_t(
                                 "To avoid these issues, create a <a>new public room</a> for the conversation " +
                                     "you plan to have.",
-                                null,
+                                undefined,
                                 {
                                     a: (sub) => (
                                         <AccessibleButton
@@ -335,15 +335,15 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
         return true;
     };
 
-    private renderHistory(): JSX.Element {
+    private renderHistory(): ReactNode {
         if (!SettingsStore.getValue(UIFeature.RoomHistorySettings)) {
             return null;
         }
 
         const client = this.context;
         const history = this.state.history;
-        const state = client.getRoom(this.props.roomId).currentState;
-        const canChangeHistory = state.mayClientSendStateEvent(EventType.RoomHistoryVisibility, client);
+        const state = client.getRoom(this.props.roomId)?.currentState;
+        const canChangeHistory = state?.mayClientSendStateEvent(EventType.RoomHistoryVisibility, client);
 
         const options = [
             {
@@ -393,8 +393,8 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
     private renderAdvanced(): JSX.Element {
         const client = this.context;
         const guestAccess = this.state.guestAccess;
-        const state = client.getRoom(this.props.roomId).currentState;
-        const canSetGuestAccess = state.mayClientSendStateEvent(EventType.RoomGuestAccess, client);
+        const state = client.getRoom(this.props.roomId)?.currentState;
+        const canSetGuestAccess = state?.mayClientSendStateEvent(EventType.RoomGuestAccess, client);
 
         return (
             <>
@@ -418,10 +418,10 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
         const client = this.context;
         const room = client.getRoom(this.props.roomId);
         const isEncrypted = this.state.encrypted;
-        const hasEncryptionPermission = room.currentState.mayClientSendStateEvent(EventType.RoomEncryption, client);
+        const hasEncryptionPermission = room?.currentState.mayClientSendStateEvent(EventType.RoomEncryption, client);
         const canEnableEncryption = !isEncrypted && hasEncryptionPermission;
 
-        let encryptionSettings = null;
+        let encryptionSettings: JSX.Element | undefined;
         if (isEncrypted && SettingsStore.isEnabled("blacklistUnverifiedDevices")) {
             encryptionSettings = (
                 <SettingsFlag
@@ -435,8 +435,8 @@ export default class SecurityRoomSettingsTab extends React.Component<IProps, ISt
 
         const historySection = this.renderHistory();
 
-        let advanced;
-        if (room.getJoinRule() === JoinRule.Public) {
+        let advanced: JSX.Element | undefined;
+        if (room?.getJoinRule() === JoinRule.Public) {
             advanced = (
                 <div className="mx_SettingsTab_section">
                     <AccessibleButton
diff --git a/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx b/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
index 0eb362830f..7a8157e38c 100644
--- a/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
+++ b/src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { ChangeEvent } from "react";
+import React, { ChangeEvent, ReactNode } from "react";
 
 import { _t } from "../../../../../languageHandler";
 import SdkConfig from "../../../../../SdkConfig";
@@ -41,8 +41,8 @@ interface IState {
     layout: Layout;
     // User profile data for the message preview
     userId?: string;
-    displayName: string;
-    avatarUrl: string;
+    displayName?: string;
+    avatarUrl?: string;
 }
 
 export default class AppearanceUserSettingsTab extends React.Component<IProps, IState> {
@@ -58,16 +58,13 @@ export default class AppearanceUserSettingsTab extends React.Component<IProps, I
             systemFont: SettingsStore.getValue("systemFont"),
             showAdvanced: false,
             layout: SettingsStore.getValue("layout"),
-            userId: null,
-            displayName: null,
-            avatarUrl: null,
         };
     }
 
     public async componentDidMount(): Promise<void> {
         // Fetch the current user profile for the message preview
         const client = MatrixClientPeg.get();
-        const userId = client.getUserId();
+        const userId = client.getUserId()!;
         const profileInfo = await client.getProfileInfo(userId);
         if (this.unmounted) return;
 
@@ -86,7 +83,7 @@ export default class AppearanceUserSettingsTab extends React.Component<IProps, I
         this.setState({ layout: layout });
     };
 
-    private renderAdvancedSection(): JSX.Element {
+    private renderAdvancedSection(): ReactNode {
         if (!SettingsStore.getValue(UIFeature.AdvancedSettings)) return null;
 
         const brand = SdkConfig.get().brand;
@@ -115,7 +112,7 @@ export default class AppearanceUserSettingsTab extends React.Component<IProps, I
                     />
                     <Field
                         className="mx_AppearanceUserSettingsTab_systemFont"
-                        label={SettingsStore.getDisplayName("systemFont")}
+                        label={SettingsStore.getDisplayName("systemFont")!}
                         onChange={(value: ChangeEvent<HTMLInputElement>) => {
                             this.setState({
                                 systemFont: value.target.value,
diff --git a/src/components/views/settings/tabs/user/HelpUserSettingsTab.tsx b/src/components/views/settings/tabs/user/HelpUserSettingsTab.tsx
index 83b81aa3fd..0134062ca6 100644
--- a/src/components/views/settings/tabs/user/HelpUserSettingsTab.tsx
+++ b/src/components/views/settings/tabs/user/HelpUserSettingsTab.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { logger } from "matrix-js-sdk/src/logger";
 
 import AccessibleButton from "../../../elements/AccessibleButton";
@@ -37,7 +37,7 @@ interface IProps {
 }
 
 interface IState {
-    appVersion: string;
+    appVersion: string | null;
     canUpdate: boolean;
 }
 
@@ -53,13 +53,13 @@ export default class HelpUserSettingsTab extends React.Component<IProps, IState>
 
     public componentDidMount(): void {
         PlatformPeg.get()
-            .getAppVersion()
+            ?.getAppVersion()
             .then((ver) => this.setState({ appVersion: ver }))
             .catch((e) => {
                 logger.error("Error getting vector version: ", e);
             });
         PlatformPeg.get()
-            .canSelfUpdate()
+            ?.canSelfUpdate()
             .then((v) => this.setState({ canUpdate: v }))
             .catch((e) => {
                 logger.error("Error getting self updatability: ", e);
@@ -90,7 +90,7 @@ export default class HelpUserSettingsTab extends React.Component<IProps, IState>
         MatrixClientPeg.get()
             .store.deleteAllData()
             .then(() => {
-                PlatformPeg.get().reload();
+                PlatformPeg.get()?.reload();
             });
     };
 
@@ -106,11 +106,11 @@ export default class HelpUserSettingsTab extends React.Component<IProps, IState>
         });
     };
 
-    private renderLegal(): JSX.Element {
+    private renderLegal(): ReactNode {
         const tocLinks = SdkConfig.get().terms_and_conditions_links;
         if (!tocLinks) return null;
 
-        const legalLinks = [];
+        const legalLinks: JSX.Element[] = [];
         for (const tocEntry of tocLinks) {
             legalLinks.push(
                 <div key={tocEntry.url}>
@@ -248,7 +248,7 @@ export default class HelpUserSettingsTab extends React.Component<IProps, IState>
             );
         }
 
-        let updateButton = null;
+        let updateButton: JSX.Element | undefined;
         if (this.state.canUpdate) {
             updateButton = <UpdateCheckButton />;
         }
diff --git a/src/components/views/settings/tabs/user/MjolnirUserSettingsTab.tsx b/src/components/views/settings/tabs/user/MjolnirUserSettingsTab.tsx
index 98d7c41f0f..6f9f538237 100644
--- a/src/components/views/settings/tabs/user/MjolnirUserSettingsTab.tsx
+++ b/src/components/views/settings/tabs/user/MjolnirUserSettingsTab.tsx
@@ -105,7 +105,7 @@ export default class MjolnirUserSettingsTab extends React.Component<{}, IState>
         this.setState({ busy: true });
         try {
             const list = Mjolnir.sharedInstance().getPersonalList();
-            await list.unbanEntity(rule.kind, rule.entity);
+            await list!.unbanEntity(rule.kind, rule.entity);
         } catch (e) {
             logger.error(e);
 
@@ -142,7 +142,7 @@ export default class MjolnirUserSettingsTab extends React.Component<{}, IState>
         const renderRules = (rules: ListRule[]): JSX.Element => {
             if (rules.length === 0) return <i>{_t("None")}</i>;
 
-            const tiles = [];
+            const tiles: JSX.Element[] = [];
             for (const rule of rules) {
                 tiles.push(
                     <li key={rule.kind + rule.entity}>
@@ -173,7 +173,7 @@ export default class MjolnirUserSettingsTab extends React.Component<{}, IState>
         const rules = list ? [...list.userRules, ...list.serverRules] : [];
         if (!list || rules.length <= 0) return <i>{_t("You have not ignored anyone.")}</i>;
 
-        const tiles = [];
+        const tiles: JSX.Element[] = [];
         for (const rule of rules) {
             tiles.push(
                 <li key={rule.entity} className="mx_MjolnirUserSettingsTab_listItem">
@@ -205,7 +205,7 @@ export default class MjolnirUserSettingsTab extends React.Component<{}, IState>
         });
         if (!lists || lists.length <= 0) return <i>{_t("You are not subscribed to any lists")}</i>;
 
-        const tiles = [];
+        const tiles: JSX.Element[] = [];
         for (const list of lists) {
             const room = MatrixClientPeg.get().getRoom(list.roomId);
             const name = room ? (
diff --git a/src/components/views/settings/tabs/user/SecurityUserSettingsTab.tsx b/src/components/views/settings/tabs/user/SecurityUserSettingsTab.tsx
index 2d2a086c61..9697af802b 100644
--- a/src/components/views/settings/tabs/user/SecurityUserSettingsTab.tsx
+++ b/src/components/views/settings/tabs/user/SecurityUserSettingsTab.tsx
@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 import { sleep } from "matrix-js-sdk/src/utils";
 import { Room, RoomEvent } from "matrix-js-sdk/src/models/room";
 import { logger } from "matrix-js-sdk/src/logger";
@@ -169,7 +169,7 @@ export default class SecurityUserSettingsTab extends React.Component<IProps, ISt
         return MatrixClientPeg.get()
             .getRooms()
             .filter((r) => {
-                return r.hasMembershipState(MatrixClientPeg.get().getUserId(), "invite");
+                return r.hasMembershipState(MatrixClientPeg.get().getUserId()!, "invite");
             });
     };
 
@@ -247,7 +247,7 @@ export default class SecurityUserSettingsTab extends React.Component<IProps, ISt
         );
     }
 
-    private renderManageInvites(): JSX.Element {
+    private renderManageInvites(): ReactNode {
         const { invitedRoomIds } = this.state;
 
         if (invitedRoomIds.size === 0) {
diff --git a/src/components/views/settings/tabs/user/VoiceUserSettingsTab.tsx b/src/components/views/settings/tabs/user/VoiceUserSettingsTab.tsx
index 65891139f3..49067d4ec1 100644
--- a/src/components/views/settings/tabs/user/VoiceUserSettingsTab.tsx
+++ b/src/components/views/settings/tabs/user/VoiceUserSettingsTab.tsx
@@ -15,7 +15,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React from "react";
+import React, { ReactNode } from "react";
 
 import { _t } from "../../../../../languageHandler";
 import MediaDeviceHandler, { IMediaDevices, MediaDeviceKindEnum } from "../../../../../MediaDeviceHandler";
@@ -28,10 +28,10 @@ import LabelledToggleSwitch from "../../../elements/LabelledToggleSwitch";
 import { requestMediaPermissions } from "../../../../../utils/media/requestMediaPermissions";
 
 interface IState {
-    mediaDevices: IMediaDevices;
-    [MediaDeviceKindEnum.AudioOutput]: string;
-    [MediaDeviceKindEnum.AudioInput]: string;
-    [MediaDeviceKindEnum.VideoInput]: string;
+    mediaDevices: IMediaDevices | null;
+    [MediaDeviceKindEnum.AudioOutput]: string | null;
+    [MediaDeviceKindEnum.AudioInput]: string | null;
+    [MediaDeviceKindEnum.VideoInput]: string | null;
     audioAutoGainControl: boolean;
     audioEchoCancellation: boolean;
     audioNoiseSuppression: boolean;
@@ -104,7 +104,7 @@ export default class VoiceUserSettingsTab extends React.Component<{}, IState> {
         });
     }
 
-    private renderDropdown(kind: MediaDeviceKindEnum, label: string): JSX.Element {
+    private renderDropdown(kind: MediaDeviceKindEnum, label: string): ReactNode {
         const devices = this.state.mediaDevices[kind].slice(0);
         if (devices.length === 0) return null;
 
@@ -121,11 +121,11 @@ export default class VoiceUserSettingsTab extends React.Component<{}, IState> {
         );
     }
 
-    public render(): React.ReactNode {
-        let requestButton = null;
-        let speakerDropdown = null;
-        let microphoneDropdown = null;
-        let webcamDropdown = null;
+    public render(): ReactNode {
+        let requestButton: ReactNode | undefined;
+        let speakerDropdown: ReactNode | undefined;
+        let microphoneDropdown: ReactNode | undefined;
+        let webcamDropdown: ReactNode | undefined;
         if (!this.state.mediaDevices) {
             requestButton = (
                 <div className="mx_VoiceUserSettingsTab_missingMediaPermissions">
diff --git a/src/components/views/spaces/QuickSettingsButton.tsx b/src/components/views/spaces/QuickSettingsButton.tsx
index 4fc35da5a7..1adcd41960 100644
--- a/src/components/views/spaces/QuickSettingsButton.tsx
+++ b/src/components/views/spaces/QuickSettingsButton.tsx
@@ -46,8 +46,8 @@ const QuickSettingsButton: React.FC<{
     const { [MetaSpace.Favourites]: favouritesEnabled, [MetaSpace.People]: peopleEnabled } =
         useSettingValue<Record<MetaSpace, boolean>>("Spaces.enabledMetaSpaces");
 
-    let contextMenu: JSX.Element;
-    if (menuDisplayed) {
+    let contextMenu: JSX.Element | undefined;
+    if (menuDisplayed && handle.current) {
         contextMenu = (
             <ContextMenu
                 {...alwaysAboveRightOf(handle.current.getBoundingClientRect(), ChevronFace.None, 16)}
diff --git a/src/components/views/spaces/SpaceSettingsGeneralTab.tsx b/src/components/views/spaces/SpaceSettingsGeneralTab.tsx
index 5ff2c77f7c..2215d148f6 100644
--- a/src/components/views/spaces/SpaceSettingsGeneralTab.tsx
+++ b/src/components/views/spaces/SpaceSettingsGeneralTab.tsx
@@ -38,9 +38,9 @@ const SpaceSettingsGeneralTab: React.FC<IProps> = ({ matrixClient: cli, space, o
     const [busy, setBusy] = useState(false);
     const [error, setError] = useState("");
 
-    const userId = cli.getUserId();
+    const userId = cli.getUserId()!;
 
-    const [newAvatar, setNewAvatar] = useState<File>(null); // undefined means to remove avatar
+    const [newAvatar, setNewAvatar] = useState<File | null | undefined>(null); // undefined means to remove avatar
     const canSetAvatar = space.currentState.maySendStateEvent(EventType.RoomAvatar, userId);
     const avatarChanged = newAvatar !== null;
 
@@ -48,8 +48,8 @@ const SpaceSettingsGeneralTab: React.FC<IProps> = ({ matrixClient: cli, space, o
     const canSetName = space.currentState.maySendStateEvent(EventType.RoomName, userId);
     const nameChanged = name !== space.name;
 
-    const currentTopic = getTopic(space)?.text;
-    const [topic, setTopic] = useState<string>(currentTopic);
+    const currentTopic = getTopic(space)?.text ?? "";
+    const [topic, setTopic] = useState(currentTopic);
     const canSetTopic = space.currentState.maySendStateEvent(EventType.RoomTopic, userId);
     const topicChanged = topic !== currentTopic;
 
@@ -104,7 +104,7 @@ const SpaceSettingsGeneralTab: React.FC<IProps> = ({ matrixClient: cli, space, o
 
             <div className="mx_SettingsTab_section">
                 <SpaceBasicSettings
-                    avatarUrl={avatarUrlForRoom(space, 80, 80, "crop")}
+                    avatarUrl={avatarUrlForRoom(space, 80, 80, "crop") ?? undefined}
                     avatarDisabled={busy || !canSetAvatar}
                     setAvatar={setNewAvatar}
                     name={name}
diff --git a/src/components/views/spaces/SpaceSettingsVisibilityTab.tsx b/src/components/views/spaces/SpaceSettingsVisibilityTab.tsx
index 98c2c6b087..35f310dbdd 100644
--- a/src/components/views/spaces/SpaceSettingsVisibilityTab.tsx
+++ b/src/components/views/spaces/SpaceSettingsVisibilityTab.tsx
@@ -47,7 +47,7 @@ const SpaceSettingsVisibilityTab: React.FC<IProps> = ({ matrixClient: cli, space
         false,
     );
 
-    const userId = cli.getUserId();
+    const userId = cli.getUserId()!;
 
     const joinRule = useRoomState(space, (state) => state.getJoinRule());
     const [guestAccessEnabled, setGuestAccessEnabled] = useLocalEcho<boolean>(
@@ -120,7 +120,7 @@ const SpaceSettingsVisibilityTab: React.FC<IProps> = ({ matrixClient: cli, space
         );
     }
 
-    let addressesSection;
+    let addressesSection: JSX.Element | undefined;
     if (space.getJoinRule() === JoinRule.Public) {
         addressesSection = (
             <>
@@ -129,7 +129,7 @@ const SpaceSettingsVisibilityTab: React.FC<IProps> = ({ matrixClient: cli, space
                     roomId={space.roomId}
                     canSetCanonicalAlias={canSetCanonical}
                     canSetAliases={true}
-                    canonicalAliasEvent={canonicalAliasEv}
+                    canonicalAliasEvent={canonicalAliasEv ?? undefined}
                     hidePublishSetting={!serverSupportsExploringSpaces}
                 />
             </>
diff --git a/src/components/views/terms/InlineTermsAgreement.tsx b/src/components/views/terms/InlineTermsAgreement.tsx
index 26880ce1ce..17357ee0b4 100644
--- a/src/components/views/terms/InlineTermsAgreement.tsx
+++ b/src/components/views/terms/InlineTermsAgreement.tsx
@@ -83,7 +83,7 @@ export default class InlineTermsAgreement extends React.Component<IProps, IState
     };
 
     private renderCheckboxes(): React.ReactNode[] {
-        const rendered = [];
+        const rendered: JSX.Element[] = [];
         for (let i = 0; i < this.state.policies.length; i++) {
             const policy = this.state.policies[i];
             const introText = _t(
diff --git a/src/components/views/toasts/VerificationRequestToast.tsx b/src/components/views/toasts/VerificationRequestToast.tsx
index e2a4612954..b1f76d2d2a 100644
--- a/src/components/views/toasts/VerificationRequestToast.tsx
+++ b/src/components/views/toasts/VerificationRequestToast.tsx
@@ -77,7 +77,7 @@ export default class VerificationRequestToast extends React.PureComponent<IProps
             const device = await cli.getDevice(request.channel.deviceId);
             const ip = device.last_seen_ip;
             this.setState({
-                device: cli.getStoredDevice(cli.getUserId(), request.channel.deviceId),
+                device: cli.getStoredDevice(cli.getUserId()!, request.channel.deviceId),
                 ip,
             });
         }
@@ -137,7 +137,7 @@ export default class VerificationRequestToast extends React.PureComponent<IProps
                             request.cancel();
                         },
                     },
-                    null,
+                    undefined,
                     /* priority = */ false,
                     /* static = */ true,
                 );
diff --git a/src/components/views/user-onboarding/UserOnboardingButton.tsx b/src/components/views/user-onboarding/UserOnboardingButton.tsx
index 241ade8ed1..b2825bbd28 100644
--- a/src/components/views/user-onboarding/UserOnboardingButton.tsx
+++ b/src/components/views/user-onboarding/UserOnboardingButton.tsx
@@ -39,7 +39,7 @@ export function UserOnboardingButton({ selected, minimized }: Props): JSX.Elemen
     const visible = useSettingValue<boolean>("FTUE.userOnboardingButton");
 
     if (!visible || minimized || !showUserOnboardingPage(useCase)) {
-        return null;
+        return <></>;
     }
 
     return <UserOnboardingButtonInternal selected={selected} minimized={minimized} />;
diff --git a/src/components/views/user-onboarding/UserOnboardingFeedback.tsx b/src/components/views/user-onboarding/UserOnboardingFeedback.tsx
index d5e6fd9181..ee827e2603 100644
--- a/src/components/views/user-onboarding/UserOnboardingFeedback.tsx
+++ b/src/components/views/user-onboarding/UserOnboardingFeedback.tsx
@@ -26,7 +26,7 @@ import { shouldShowFeedback } from "../../../utils/Feedback";
 
 export function UserOnboardingFeedback(): JSX.Element {
     if (!shouldShowFeedback()) {
-        return null;
+        return <></>;
     }
 
     return (
diff --git a/src/components/views/user-onboarding/UserOnboardingTask.tsx b/src/components/views/user-onboarding/UserOnboardingTask.tsx
index 7b7b8e5346..1c1e3b2544 100644
--- a/src/components/views/user-onboarding/UserOnboardingTask.tsx
+++ b/src/components/views/user-onboarding/UserOnboardingTask.tsx
@@ -57,7 +57,7 @@ export function UserOnboardingTask({ task, completed = false }: Props): JSX.Elem
                     kind="primary_outline"
                     href={task.action.href}
                     target="_blank"
-                    onClick={task.action.onClick}
+                    onClick={task.action.onClick ?? null}
                 >
                     {task.action.label}
                 </AccessibleButton>
diff --git a/src/components/views/voip/CallView.tsx b/src/components/views/voip/CallView.tsx
index a8437129a7..e1dac478b3 100644
--- a/src/components/views/voip/CallView.tsx
+++ b/src/components/views/voip/CallView.tsx
@@ -150,7 +150,7 @@ export const Lobby: FC<LobbyProps> = ({ room, joinCallButtonDisabledTooltip, con
     }, [videoMuted, setVideoMuted]);
 
     const [videoStream, audioInputs, videoInputs] = useAsyncMemo(
-        async (): Promise<[MediaStream, MediaDeviceInfo[], MediaDeviceInfo[]]> => {
+        async (): Promise<[MediaStream | null, MediaDeviceInfo[], MediaDeviceInfo[]]> => {
             let devices = await MediaDeviceHandler.getDevices();
 
             // We get the preview stream before requesting devices: this is because
@@ -335,7 +335,7 @@ const StartCallView: FC<StartCallViewProps> = ({ room, resizing, call, setStarti
                 <AppTile
                     app={call.widget}
                     room={room}
-                    userId={cli.credentials.userId}
+                    userId={cli.credentials.userId!}
                     creatorUserId={call.widget.creatorUserId}
                     waitForIframeLoad={call.widget.waitForIframeLoad}
                     showMenubar={false}
@@ -402,7 +402,7 @@ const JoinCallView: FC<JoinCallViewProps> = ({ room, resizing, call }) => {
             <AppTile
                 app={call.widget}
                 room={room}
-                userId={cli.credentials.userId}
+                userId={cli.credentials.userId!}
                 creatorUserId={call.widget.creatorUserId}
                 waitForIframeLoad={call.widget.waitForIframeLoad}
                 showMenubar={false}
diff --git a/src/components/views/voip/LegacyCallView.tsx b/src/components/views/voip/LegacyCallView.tsx
index 5b04304208..41ad1897a2 100644
--- a/src/components/views/voip/LegacyCallView.tsx
+++ b/src/components/views/voip/LegacyCallView.tsx
@@ -180,7 +180,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         }
     };
 
-    private updateCallListeners(oldCall: MatrixCall, newCall: MatrixCall): void {
+    private updateCallListeners(oldCall: MatrixCall, newCall: MatrixCall | null): void {
         if (oldCall === newCall) return;
 
         if (oldCall) {
@@ -430,7 +430,7 @@ export default class LegacyCallView extends React.Component<IProps, IState> {
         const { pipMode, call, onResize } = this.props;
         const { isLocalOnHold, isRemoteOnHold, sidebarShown, primaryFeed, secondaryFeed, sidebarFeeds } = this.state;
 
-        const callRoom = MatrixClientPeg.get().getRoom(call.roomId);
+        const callRoom = MatrixClientPeg.get().getRoom(call.roomId) ?? undefined;
         const avatarSize = pipMode ? 76 : 160;
         const transfereeCall = LegacyCallHandler.instance.getTransfereeForCallId(call.callId);
         const isOnHold = isLocalOnHold || isRemoteOnHold;
diff --git a/src/editor/dom.ts b/src/editor/dom.ts
index a48cace4ef..19bccdbef7 100644
--- a/src/editor/dom.ts
+++ b/src/editor/dom.ts
@@ -190,6 +190,8 @@ function getTextAndOffsetToNode(editor: HTMLDivElement, selectionNode: Node): {
 // get text value of text node, ignoring ZWS if it's a caret node
 function getTextNodeValue(node: Node): string {
     const nodeText = node.nodeValue;
+    if (!nodeText) return "";
+
     // filter out ZWS for caret nodes
     if (isCaretNode(node.parentElement)) {
         // typed in the caret node, so there is now something more in it than the ZWS
@@ -200,9 +202,9 @@ function getTextNodeValue(node: Node): string {
             // only contains ZWS, which is ignored, so return empty string
             return "";
         }
-    } else {
-        return nodeText;
     }
+
+    return nodeText;
 }
 
 export function getRangeForSelection(editor: HTMLDivElement, model: EditorModel, selection: Selection): Range {
diff --git a/src/editor/parts.ts b/src/editor/parts.ts
index 74203b586e..d5a5c39988 100644
--- a/src/editor/parts.ts
+++ b/src/editor/parts.ts
@@ -424,7 +424,7 @@ class RoomPillPart extends PillPart {
         let initialLetter = "";
         let avatarUrl = Avatar.avatarUrlForRoom(this.room, 16, 16, "crop");
         if (!avatarUrl) {
-            initialLetter = Avatar.getInitialLetter(this.room?.name || this.resourceId);
+            initialLetter = Avatar.getInitialLetter(this.room?.name || this.resourceId) ?? "";
             avatarUrl = Avatar.defaultAvatarUrlForString(this.room?.roomId ?? this.resourceId);
         }
         this.setAvatarVars(node, avatarUrl, initialLetter);
@@ -478,7 +478,7 @@ class UserPillPart extends PillPart {
         const avatarUrl = Avatar.avatarUrlForMember(this.member, 16, 16, "crop");
         let initialLetter = "";
         if (avatarUrl === defaultAvatarUrl) {
-            initialLetter = Avatar.getInitialLetter(name);
+            initialLetter = Avatar.getInitialLetter(name) ?? "";
         }
         this.setAvatarVars(node, avatarUrl, initialLetter);
     }
diff --git a/src/hooks/useAsyncMemo.ts b/src/hooks/useAsyncMemo.ts
index c1d4a55cbb..69783c88e3 100644
--- a/src/hooks/useAsyncMemo.ts
+++ b/src/hooks/useAsyncMemo.ts
@@ -18,7 +18,9 @@ import { useState, useEffect, DependencyList } from "react";
 
 type Fn<T> = () => Promise<T>;
 
-export const useAsyncMemo = <T>(fn: Fn<T>, deps: DependencyList, initialValue?: T): T | undefined => {
+export function useAsyncMemo<T>(fn: Fn<T>, deps: DependencyList, initialValue: T): T;
+export function useAsyncMemo<T>(fn: Fn<T>, deps: DependencyList, initialValue?: T): T | undefined;
+export function useAsyncMemo<T>(fn: Fn<T>, deps: DependencyList, initialValue?: T): T | undefined {
     const [value, setValue] = useState<T | undefined>(initialValue);
     useEffect(() => {
         let discard = false;
@@ -32,4 +34,4 @@ export const useAsyncMemo = <T>(fn: Fn<T>, deps: DependencyList, initialValue?:
         };
     }, deps); // eslint-disable-line react-hooks/exhaustive-deps
     return value;
-};
+}
diff --git a/src/hooks/useUserOnboardingTasks.ts b/src/hooks/useUserOnboardingTasks.ts
index e7afdacb56..beff1e111c 100644
--- a/src/hooks/useUserOnboardingTasks.ts
+++ b/src/hooks/useUserOnboardingTasks.ts
@@ -37,7 +37,7 @@ interface UserOnboardingTask {
     relevant?: UseCase[];
     action?: {
         label: string;
-        onClick?: (ev?: ButtonEvent) => void;
+        onClick?: (ev: ButtonEvent) => void;
         href?: string;
         hideOnComplete?: boolean;
     };
diff --git a/src/languageHandler.tsx b/src/languageHandler.tsx
index 2493a26966..623737175d 100644
--- a/src/languageHandler.tsx
+++ b/src/languageHandler.tsx
@@ -87,7 +87,7 @@ export function _td(s: string): string {
  * for this reason, force fallbackLocale === locale in the first call to translate
  * and fallback 'manually' so we can mark fallback strings appropriately
  * */
-const translateWithFallback = (text: string, options?: IVariables): { translated?: string; isFallback?: boolean } => {
+const translateWithFallback = (text: string, options?: IVariables): { translated: string; isFallback?: boolean } => {
     const translated = counterpart.translate(text, { ...options, fallbackLocale: counterpart.getLocale() });
     if (!translated || translated.startsWith("missing translation:")) {
         const fallbackTranslated = counterpart.translate(text, { ...options, locale: FALLBACK_LOCALE });
@@ -117,7 +117,7 @@ const translateWithFallback = (text: string, options?: IVariables): { translated
 
 // Wrapper for counterpart's translation function so that it handles nulls and undefineds properly
 // Takes the same arguments as counterpart.translate()
-function safeCounterpartTranslate(text: string, variables?: IVariables): { translated?: string; isFallback?: boolean } {
+function safeCounterpartTranslate(text: string, variables?: IVariables): { translated: string; isFallback?: boolean } {
     // Don't do substitutions in counterpart. We handle it ourselves so we can replace with React components
     // However, still pass the variables to counterpart so that it can choose the correct plural if count is given
     // It is enough to pass the count variable, but in the future counterpart might make use of other information too
@@ -251,7 +251,7 @@ export function sanitizeForTranslation(text: string): string {
  * @return a React <span> component if any non-strings were used in substitutions, otherwise a string
  */
 export function substitute(text: string, variables?: IVariables): string;
-export function substitute(text: string, variables: IVariables, tags: Tags): string;
+export function substitute(text: string, variables: IVariables | undefined, tags: Tags | undefined): string;
 export function substitute(text: string, variables?: IVariables, tags?: Tags): string | React.ReactNode {
     let result: React.ReactNode | string = text;
 
@@ -619,7 +619,7 @@ let cachedCustomTranslationsExpire = 0; // zero to trigger expiration right away
 // This awkward class exists so the test runner can get at the function. It is
 // not intended for practical or realistic usage.
 export class CustomTranslationOptions {
-    public static lookupFn: (url: string) => ICustomTranslations;
+    public static lookupFn?: (url: string) => ICustomTranslations;
 
     private constructor() {
         // static access for tests only
diff --git a/src/stores/VoiceRecordingStore.ts b/src/stores/VoiceRecordingStore.ts
index ed2b480255..e755596cc4 100644
--- a/src/stores/VoiceRecordingStore.ts
+++ b/src/stores/VoiceRecordingStore.ts
@@ -74,7 +74,7 @@ export class VoiceRecordingStore extends AsyncStoreWithClient<IState> {
      * @param {string} voiceRecordingId The room ID (with optionally the thread ID if in one) to start recording in.
      * @returns {VoiceRecording} The recording.
      */
-    public startRecording(voiceRecordingId: string): VoiceMessageRecording {
+    public startRecording(voiceRecordingId?: string): VoiceMessageRecording {
         if (!this.matrixClient) throw new Error("Cannot start a recording without a MatrixClient");
         if (!voiceRecordingId) throw new Error("Recording must be associated with a room");
         if (this.state[voiceRecordingId]) throw new Error("A recording is already in progress");
diff --git a/src/stores/widgets/StopGapWidgetDriver.ts b/src/stores/widgets/StopGapWidgetDriver.ts
index be842049b2..32f6608075 100644
--- a/src/stores/widgets/StopGapWidgetDriver.ts
+++ b/src/stores/widgets/StopGapWidgetDriver.ts
@@ -218,15 +218,15 @@ export class StopGapWidgetDriver extends WidgetDriver {
     public async sendEvent(
         eventType: string,
         content: IContent,
-        stateKey: string = null,
-        targetRoomId: string = null,
+        stateKey?: string,
+        targetRoomId?: string,
     ): Promise<ISendEventDetails> {
         const client = MatrixClientPeg.get();
         const roomId = targetRoomId || SdkContextClass.instance.roomViewStore.getRoomId();
 
         if (!client || !roomId) throw new Error("Not in a room or not attached to a client");
 
-        let r: { event_id: string } = null; // eslint-disable-line camelcase
+        let r: { event_id: string } | null = null; // eslint-disable-line camelcase
         if (stateKey !== null) {
             // state event
             r = await client.sendStateEvent(roomId, eventType, content, stateKey);
@@ -242,7 +242,7 @@ export class StopGapWidgetDriver extends WidgetDriver {
                     if (containsEmoji(content, effect.emojis)) {
                         // For initial threads launch, chat effects are disabled
                         // see #19731
-                        const isNotThread = content["m.relates_to"].rel_type !== THREAD_RELATION_TYPE.name;
+                        const isNotThread = content["m.relates_to"]?.rel_type !== THREAD_RELATION_TYPE.name;
                         if (!SettingsStore.getValue("feature_threadenabled") || isNotThread) {
                             dis.dispatch({ action: `effects.${effect.command}` });
                         }
@@ -300,7 +300,7 @@ export class StopGapWidgetDriver extends WidgetDriver {
         }
     }
 
-    private pickRooms(roomIds: (string | Symbols.AnyRoom)[] = null): Room[] {
+    private pickRooms(roomIds?: (string | Symbols.AnyRoom)[]): Room[] {
         const client = MatrixClientPeg.get();
         if (!client) throw new Error("Not attached to a client");
 
@@ -309,14 +309,14 @@ export class StopGapWidgetDriver extends WidgetDriver {
                 ? client.getVisibleRooms()
                 : roomIds.map((r) => client.getRoom(r))
             : [client.getRoom(SdkContextClass.instance.roomViewStore.getRoomId())];
-        return targetRooms.filter((r) => !!r);
+        return targetRooms.filter((r) => !!r) as Room[];
     }
 
     public async readRoomEvents(
         eventType: string,
         msgtype: string | undefined,
         limitPerRoom: number,
-        roomIds: (string | Symbols.AnyRoom)[] = null,
+        roomIds?: (string | Symbols.AnyRoom)[],
     ): Promise<IRoomEvent[]> {
         limitPerRoom = limitPerRoom > 0 ? Math.min(limitPerRoom, Number.MAX_SAFE_INTEGER) : Number.MAX_SAFE_INTEGER; // relatively arbitrary
 
@@ -343,7 +343,7 @@ export class StopGapWidgetDriver extends WidgetDriver {
         eventType: string,
         stateKey: string | undefined,
         limitPerRoom: number,
-        roomIds: (string | Symbols.AnyRoom)[] = null,
+        roomIds?: (string | Symbols.AnyRoom)[],
     ): Promise<IRoomEvent[]> {
         limitPerRoom = limitPerRoom > 0 ? Math.min(limitPerRoom, Number.MAX_SAFE_INTEGER) : Number.MAX_SAFE_INTEGER; // relatively arbitrary
 
@@ -467,8 +467,8 @@ export class StopGapWidgetDriver extends WidgetDriver {
 
         return {
             chunk: events.map((e) => e.getEffectiveEvent() as IRoomEvent),
-            nextBatch,
-            prevBatch,
+            nextBatch: nextBatch ?? undefined,
+            prevBatch: prevBatch ?? undefined,
         };
     }
 }
diff --git a/src/utils/beacon/bounds.ts b/src/utils/beacon/bounds.ts
index c7942953e4..ad1b515fb4 100644
--- a/src/utils/beacon/bounds.ts
+++ b/src/utils/beacon/bounds.ts
@@ -48,10 +48,12 @@ export const getBeaconBounds = (beacons: Beacon[]): Bounds | undefined => {
     const sortedByLat = [...coords].sort((left, right) => right.latitude - left.latitude);
     const sortedByLong = [...coords].sort((left, right) => right.longitude - left.longitude);
 
+    if (sortedByLat.length < 1 || sortedByLong.length < 1) return;
+
     return {
-        north: sortedByLat[0].latitude,
-        south: sortedByLat[sortedByLat.length - 1].latitude,
-        east: sortedByLong[0].longitude,
-        west: sortedByLong[sortedByLong.length - 1].longitude,
+        north: sortedByLat[0]!.latitude,
+        south: sortedByLat[sortedByLat.length - 1]!.latitude,
+        east: sortedByLong[0]!.longitude,
+        west: sortedByLong[sortedByLong.length - 1]!.longitude,
     };
 };
diff --git a/src/widgets/CapabilityText.tsx b/src/widgets/CapabilityText.tsx
index d39c2171b2..d0dffd399e 100644
--- a/src/widgets/CapabilityText.tsx
+++ b/src/widgets/CapabilityText.tsx
@@ -135,7 +135,7 @@ export class CapabilityText {
         // First see if we have a super simple line of text to provide back
         if (CapabilityText.simpleCaps[capability]) {
             const textForKind = CapabilityText.simpleCaps[capability];
-            if (textForKind[kind]) return { primary: _t(textForKind[kind]) };
+            if (textForKind[kind]) return { primary: _t(textForKind[kind]!) };
             if (textForKind[GENERIC_WIDGET_KIND]) return { primary: _t(textForKind[GENERIC_WIDGET_KIND]) };
 
             // ... we'll fall through to the generic capability processing at the end of this
@@ -195,8 +195,8 @@ export class CapabilityText {
                     : CapabilityText.nonStateSendRecvCaps;
             if (evSendRecv[eventCap.eventType]) {
                 const textForKind = evSendRecv[eventCap.eventType];
-                const textForDirection = textForKind[kind] || textForKind[GENERIC_WIDGET_KIND];
-                if (textForDirection && textForDirection[eventCap.direction]) {
+                const textForDirection = textForKind?.[kind] || textForKind?.[GENERIC_WIDGET_KIND];
+                if (textForDirection?.[eventCap.direction]) {
                     return {
                         primary: _t(textForDirection[eventCap.direction]),
                         // no byline because we would have already represented the event properly
diff --git a/src/widgets/Jitsi.ts b/src/widgets/Jitsi.ts
index 5ab3e98a8c..c98f3a4b79 100644
--- a/src/widgets/Jitsi.ts
+++ b/src/widgets/Jitsi.ts
@@ -87,7 +87,7 @@ export class Jitsi {
      * @param {string} url The URL to parse.
      * @returns {JitsiWidgetData} The widget data if eligible, otherwise null.
      */
-    public parsePreferredConferenceUrl(url: string): JitsiWidgetData {
+    public parsePreferredConferenceUrl(url: string): JitsiWidgetData | null {
         const parsed = new URL(url);
         if (parsed.hostname !== this.preferredDomain) return null; // invalid
         return {
diff --git a/test/PosthogAnalytics-test.ts b/test/PosthogAnalytics-test.ts
index 07f3f51dfb..5188bd9a1f 100644
--- a/test/PosthogAnalytics-test.ts
+++ b/test/PosthogAnalytics-test.ts
@@ -57,7 +57,7 @@ describe("PosthogAnalytics", () => {
                 digest: async (_: AlgorithmIdentifier, encodedMessage: BufferSource) => {
                     const message = new TextDecoder().decode(encodedMessage);
                     const hexHash = shaHashes[message];
-                    const bytes = [];
+                    const bytes: number[] = [];
                     for (let c = 0; c < hexHash.length; c += 2) {
                         bytes.push(parseInt(hexHash.slice(c, c + 2), 16));
                     }
@@ -68,6 +68,7 @@ describe("PosthogAnalytics", () => {
     });
 
     afterEach(() => {
+        // @ts-ignore
         window.crypto = null;
         SdkConfig.unset(); // we touch the config, so clean up
     });
@@ -116,7 +117,7 @@ describe("PosthogAnalytics", () => {
                 foo: "bar",
             });
             expect(mocked(fakePosthog).capture.mock.calls[0][0]).toBe("JestTestEvents");
-            expect(mocked(fakePosthog).capture.mock.calls[0][1]["foo"]).toEqual("bar");
+            expect(mocked(fakePosthog).capture.mock.calls[0][1]!["foo"]).toEqual("bar");
         });
 
         it("Should not track events if anonymous", async () => {
@@ -209,7 +210,7 @@ describe("PosthogAnalytics", () => {
             analytics.trackEvent<ITestEvent>({
                 eventName: "JestTestEvents",
             });
-            expect(mocked(fakePosthog).capture.mock.calls[0][1]["$set"]).toStrictEqual({
+            expect(mocked(fakePosthog).capture.mock.calls[0][1]!["$set"]).toStrictEqual({
                 WebLayout: "IRC",
             });
         });
@@ -226,7 +227,7 @@ describe("PosthogAnalytics", () => {
             analytics.trackEvent<ITestEvent>({
                 eventName: "JestTestEvents",
             });
-            expect(mocked(fakePosthog).capture.mock.calls[0][1]["$set"]).toStrictEqual({
+            expect(mocked(fakePosthog).capture.mock.calls[0][1]!["$set"]).toStrictEqual({
                 WebLayout: "Bubble",
             });
         });
@@ -243,7 +244,7 @@ describe("PosthogAnalytics", () => {
             analytics.trackEvent<ITestEvent>({
                 eventName: "JestTestEvents",
             });
-            expect(mocked(fakePosthog).capture.mock.calls[0][1]["$set"]).toStrictEqual({
+            expect(mocked(fakePosthog).capture.mock.calls[0][1]!["$set"]).toStrictEqual({
                 WebLayout: "Group",
             });
         });
@@ -261,7 +262,7 @@ describe("PosthogAnalytics", () => {
             analytics.trackEvent<ITestEvent>({
                 eventName: "JestTestEvents",
             });
-            expect(mocked(fakePosthog).capture.mock.calls[0][1]["$set"]).toStrictEqual({
+            expect(mocked(fakePosthog).capture.mock.calls[0][1]!["$set"]).toStrictEqual({
                 WebLayout: "Compact",
             });
         });
diff --git a/test/ScalarAuthClient-test.ts b/test/ScalarAuthClient-test.ts
index 00b1d0644b..9dad8e2459 100644
--- a/test/ScalarAuthClient-test.ts
+++ b/test/ScalarAuthClient-test.ts
@@ -53,7 +53,7 @@ describe("ScalarAuthClient", function () {
         client.getOpenIdToken = jest.fn().mockResolvedValue(tokenObject);
 
         sac.exchangeForScalarToken = jest.fn((arg) => {
-            if (arg === tokenObject) return Promise.resolve("wokentoken");
+            return Promise.resolve(arg === tokenObject ? "wokentoken" : "othertoken");
         });
 
         await sac.connect();
diff --git a/test/SlashCommands-test.tsx b/test/SlashCommands-test.tsx
index 4ed059e9f3..d3d76e350d 100644
--- a/test/SlashCommands-test.tsx
+++ b/test/SlashCommands-test.tsx
@@ -223,7 +223,7 @@ describe("SlashCommands", () => {
             const command = getCommand("/part #foo:bar");
             expect(command.cmd).toBeDefined();
             expect(command.args).toBeDefined();
-            await command.cmd!.run("room-id", null, command.args);
+            await command.cmd!.run("room-id", null, command.args!);
             expect(client.leaveRoomChain).toHaveBeenCalledWith("room-id", expect.anything());
         });
     });
@@ -232,7 +232,7 @@ describe("SlashCommands", () => {
         const command = findCommand(commandName)!;
 
         it("should return usage if no args", () => {
-            expect(command.run(roomId, null).error).toBe(command.getUsage());
+            expect(command.run(roomId, null, undefined).error).toBe(command.getUsage());
         });
 
         it("should make things rainbowy", () => {
diff --git a/test/SlidingSyncManager-test.ts b/test/SlidingSyncManager-test.ts
index 1829fc2958..1918366383 100644
--- a/test/SlidingSyncManager-test.ts
+++ b/test/SlidingSyncManager-test.ts
@@ -58,7 +58,7 @@ describe("SlidingSyncManager", () => {
                     event_id: "$abc123",
                     sender: client.getUserId()!,
                     content: {
-                        creator: client.getUserId(),
+                        creator: client.getUserId()!,
                     },
                 }),
             ]);
diff --git a/test/audio/VoiceMessageRecording-test.ts b/test/audio/VoiceMessageRecording-test.ts
index e109c61ab9..94fca82bce 100644
--- a/test/audio/VoiceMessageRecording-test.ts
+++ b/test/audio/VoiceMessageRecording-test.ts
@@ -125,7 +125,7 @@ describe("VoiceMessageRecording", () => {
         const encryptedFile = {} as unknown as IEncryptedFile;
 
         beforeEach(() => {
-            voiceRecording.onDataAvailable(testBuf);
+            voiceRecording.onDataAvailable!(testBuf);
         });
 
         it("contentLength should return the buffer length", () => {
@@ -143,9 +143,9 @@ describe("VoiceMessageRecording", () => {
         });
 
         describe("upload", () => {
-            let uploadFileClient: MatrixClient;
-            let uploadFileRoomId: string;
-            let uploadBlob: Blob;
+            let uploadFileClient: MatrixClient | null;
+            let uploadFileRoomId: string | null;
+            let uploadBlob: Blob | null;
 
             beforeEach(() => {
                 uploadFileClient = null;
@@ -182,8 +182,8 @@ describe("VoiceMessageRecording", () => {
                 expect(mocked(uploadFile)).toHaveBeenCalled();
                 expect(uploadFileClient).toBe(client);
                 expect(uploadFileRoomId).toBe(roomId);
-                expect(uploadBlob.type).toBe(contentType);
-                const blobArray = await uploadBlob.arrayBuffer();
+                expect(uploadBlob?.type).toBe(contentType);
+                const blobArray = await uploadBlob!.arrayBuffer();
                 expect(new Uint8Array(blobArray)).toEqual(testBuf);
             });
 
diff --git a/test/components/structures/RoomView-test.tsx b/test/components/structures/RoomView-test.tsx
index e9860f5bba..704dc5f66b 100644
--- a/test/components/structures/RoomView-test.tsx
+++ b/test/components/structures/RoomView-test.tsx
@@ -79,7 +79,7 @@ describe("RoomView", () => {
         stores.client = cli;
         stores.rightPanelStore.useUnitTestClient(cli);
 
-        jest.spyOn(VoipUserMapper.sharedInstance(), "getVirtualRoomForRoom").mockResolvedValue(null);
+        jest.spyOn(VoipUserMapper.sharedInstance(), "getVirtualRoomForRoom").mockResolvedValue(undefined);
     });
 
     afterEach(async () => {
@@ -175,7 +175,7 @@ describe("RoomView", () => {
             instance = await getRoomViewInstance();
             oldRoom = new Room("!old:example.com", cli, cli.getSafeUserId());
             rooms.set(oldRoom.roomId, oldRoom);
-            jest.spyOn(room, "findPredecessor").mockReturnValue({ roomId: oldRoom.roomId, eventId: null });
+            jest.spyOn(room, "findPredecessor").mockReturnValue({ roomId: oldRoom.roomId });
         });
 
         it("and it has 0 unreads, getHiddenHighlightCount should return 0", async () => {
diff --git a/test/components/structures/auth/Login-test.tsx b/test/components/structures/auth/Login-test.tsx
index 8814cd04af..bf9e8d567c 100644
--- a/test/components/structures/auth/Login-test.tsx
+++ b/test/components/structures/auth/Login-test.tsx
@@ -181,7 +181,7 @@ describe("Login", function () {
         const { container, rerender } = render(getRawComponent());
         await waitForElementToBeRemoved(() => screen.queryAllByLabelText("Loading…"));
 
-        fireEvent.click(container.querySelector(".mx_SSOButton"));
+        fireEvent.click(container.querySelector(".mx_SSOButton")!);
         expect(platform.startSingleSignOn.mock.calls[0][0].baseUrl).toBe("https://matrix.org");
 
         fetchMock.get("https://server2/_matrix/client/versions", {
@@ -190,7 +190,7 @@ describe("Login", function () {
         });
         rerender(getRawComponent("https://server2"));
 
-        fireEvent.click(container.querySelector(".mx_SSOButton"));
+        fireEvent.click(container.querySelector(".mx_SSOButton")!);
         expect(platform.startSingleSignOn.mock.calls[1][0].baseUrl).toBe("https://server2");
     });
 
diff --git a/test/components/structures/auth/Registration-test.tsx b/test/components/structures/auth/Registration-test.tsx
index 85401566ba..16b64bc393 100644
--- a/test/components/structures/auth/Registration-test.tsx
+++ b/test/components/structures/auth/Registration-test.tsx
@@ -118,7 +118,7 @@ describe("Registration", function () {
         const { container, rerender } = render(getRawComponent());
         await waitForElementToBeRemoved(() => screen.queryAllByLabelText("Loading…"));
 
-        fireEvent.click(container.querySelector(".mx_SSOButton"));
+        fireEvent.click(container.querySelector(".mx_SSOButton")!);
         expect(registerRequest.mock.instances[0].baseUrl).toBe("https://matrix.org");
 
         fetchMock.get("https://server2/_matrix/client/versions", {
@@ -128,7 +128,7 @@ describe("Registration", function () {
         rerender(getRawComponent("https://server2"));
         await waitForElementToBeRemoved(() => screen.queryAllByLabelText("Loading…"));
 
-        fireEvent.click(container.querySelector(".mx_SSOButton"));
+        fireEvent.click(container.querySelector(".mx_SSOButton")!);
         expect(registerRequest.mock.instances[1].baseUrl).toBe("https://server2");
     });
 });
diff --git a/test/components/views/beacon/BeaconListItem-test.tsx b/test/components/views/beacon/BeaconListItem-test.tsx
index b6fe38ea74..580c247b69 100644
--- a/test/components/views/beacon/BeaconListItem-test.tsx
+++ b/test/components/views/beacon/BeaconListItem-test.tsx
@@ -84,7 +84,7 @@ describe("<BeaconListItem />", () => {
 
         const member = new RoomMember(roomId, aliceId);
         member.name = `Alice`;
-        const room = mockClient.getRoom(roomId);
+        const room = mockClient.getRoom(roomId)!;
         jest.spyOn(room, "getMember").mockReturnValue(member);
 
         return beacons;
@@ -185,7 +185,7 @@ describe("<BeaconListItem />", () => {
                 const { container } = getComponent({ beacon, onClick });
 
                 // click the beacon name
-                fireEvent.click(container.querySelector(".mx_BeaconStatus_description"));
+                fireEvent.click(container.querySelector(".mx_BeaconStatus_description")!);
                 expect(onClick).toHaveBeenCalled();
             });
         });
diff --git a/test/components/views/beacon/ShareLatestLocation-test.tsx b/test/components/views/beacon/ShareLatestLocation-test.tsx
index 11538f5375..654b3dc73a 100644
--- a/test/components/views/beacon/ShareLatestLocation-test.tsx
+++ b/test/components/views/beacon/ShareLatestLocation-test.tsx
@@ -47,7 +47,7 @@ describe("<ShareLatestLocation />", () => {
         const { container, asFragment } = getComponent();
         expect(asFragment()).toMatchSnapshot();
 
-        fireEvent.click(container.querySelector(".mx_CopyableText_copyButton"));
+        fireEvent.click(container.querySelector(".mx_CopyableText_copyButton")!);
         await flushPromises();
 
         expect(copyPlaintext).toHaveBeenCalledWith("51,42");
diff --git a/test/components/views/context_menus/MessageContextMenu-test.tsx b/test/components/views/context_menus/MessageContextMenu-test.tsx
index 91ee949879..7e0a532917 100644
--- a/test/components/views/context_menus/MessageContextMenu-test.tsx
+++ b/test/components/views/context_menus/MessageContextMenu-test.tsx
@@ -575,7 +575,7 @@ function createMenu(
 
     return mount(
         <RoomContext.Provider value={context as IRoomState}>
-            <MessageContextMenu chevronFace={null} mxEvent={mxEvent} onFinished={jest.fn()} {...props} />
+            <MessageContextMenu mxEvent={mxEvent} onFinished={jest.fn()} {...props} />
         </RoomContext.Provider>,
     );
 }
diff --git a/test/components/views/dialogs/AccessSecretStorageDialog-test.tsx b/test/components/views/dialogs/AccessSecretStorageDialog-test.tsx
index 3453d4e24a..4ce8337080 100644
--- a/test/components/views/dialogs/AccessSecretStorageDialog-test.tsx
+++ b/test/components/views/dialogs/AccessSecretStorageDialog-test.tsx
@@ -32,7 +32,6 @@ describe("AccessSecretStorageDialog", () => {
     const defaultProps: ComponentProps<typeof AccessSecretStorageDialog> = {
         onFinished: jest.fn(),
         checkPrivateKey: jest.fn(),
-        keyInfo: undefined,
     };
 
     const renderComponent = (props = {}): void => {
diff --git a/test/components/views/elements/EventListSummary-test.tsx b/test/components/views/elements/EventListSummary-test.tsx
index 145d62a7e2..4ecb963ee0 100644
--- a/test/components/views/elements/EventListSummary-test.tsx
+++ b/test/components/views/elements/EventListSummary-test.tsx
@@ -66,11 +66,11 @@ describe("EventListSummary", function () {
     }
     const generateMembershipEvent = (
         eventId: string,
-        { senderId, userId, membership, prevMembership }: MembershipEventParams,
+        { senderId, userId, membership, prevMembership }: MembershipEventParams & { userId: string },
     ): MatrixEvent => {
         const member = new RoomMember(roomId, userId);
         // Use localpart as display name;
-        member.name = userId.match(/@([^:]*):/)[1];
+        member.name = userId.match(/@([^:]*):/)![1];
         jest.spyOn(member, "getAvatarUrl").mockReturnValue("avatar.jpeg");
         jest.spyOn(member, "getMxcAvatarUrl").mockReturnValue("mxc://avatar.url/image.png");
         const e = mkMembership({
@@ -89,8 +89,8 @@ describe("EventListSummary", function () {
     };
 
     // Generate mock MatrixEvents from the array of parameters
-    const generateEvents = (parameters: MembershipEventParams[]) => {
-        const res = [];
+    const generateEvents = (parameters: Array<MembershipEventParams & { userId: string }>) => {
+        const res: MatrixEvent[] = [];
         for (let i = 0; i < parameters.length; i++) {
             res.push(generateMembershipEvent(`event${i}`, parameters[i]));
         }
@@ -108,7 +108,9 @@ describe("EventListSummary", function () {
             events.forEach((e) => {
                 e.userId = userId;
             });
-            eventsForUsers = eventsForUsers.concat(generateEvents(events));
+            eventsForUsers = eventsForUsers.concat(
+                generateEvents(events as Array<MembershipEventParams & { userId: string }>),
+            );
         }
         return eventsForUsers;
     };
diff --git a/test/components/views/elements/LearnMore-test.tsx b/test/components/views/elements/LearnMore-test.tsx
index 98241b1ae1..b527713ec3 100644
--- a/test/components/views/elements/LearnMore-test.tsx
+++ b/test/components/views/elements/LearnMore-test.tsx
@@ -29,7 +29,10 @@ describe("<LearnMore />", () => {
     };
     const getComponent = (props = {}) => <LearnMore {...defaultProps} {...props} />;
 
-    const modalSpy = jest.spyOn(Modal, "createDialog").mockReturnValue(undefined);
+    const modalSpy = jest.spyOn(Modal, "createDialog").mockReturnValue({
+        finished: new Promise(() => {}),
+        close: jest.fn(),
+    });
 
     beforeEach(() => {
         jest.clearAllMocks();
diff --git a/test/components/views/elements/TooltipTarget-test.tsx b/test/components/views/elements/TooltipTarget-test.tsx
index 09438fc2e5..82b620c262 100644
--- a/test/components/views/elements/TooltipTarget-test.tsx
+++ b/test/components/views/elements/TooltipTarget-test.tsx
@@ -36,7 +36,7 @@ describe("<TooltipTarget />", () => {
         // clean up renderer tooltips
         const wrapper = document.querySelector(".mx_Tooltip_wrapper");
         while (wrapper?.firstChild) {
-            wrapper.removeChild(wrapper.lastChild);
+            wrapper.removeChild(wrapper.lastChild!);
         }
     });
 
diff --git a/test/components/views/messages/MKeyVerificationConclusion-test.tsx b/test/components/views/messages/MKeyVerificationConclusion-test.tsx
index 03966d1673..c19166ef57 100644
--- a/test/components/views/messages/MKeyVerificationConclusion-test.tsx
+++ b/test/components/views/messages/MKeyVerificationConclusion-test.tsx
@@ -50,10 +50,10 @@ describe("MKeyVerificationConclusion", () => {
     }) => {
         class MockVerificationRequest extends EventEmitter {
             constructor(
-                public readonly pending: boolean,
-                public readonly cancelled: boolean,
-                public readonly done: boolean,
-                public readonly otherUserId: string,
+                public readonly pending?: boolean,
+                public readonly cancelled?: boolean,
+                public readonly done?: boolean,
+                public readonly otherUserId?: string,
             ) {
                 super();
             }
diff --git a/test/components/views/messages/MLocationBody-test.tsx b/test/components/views/messages/MLocationBody-test.tsx
index 3f748fbaf7..a3f707a734 100644
--- a/test/components/views/messages/MLocationBody-test.tsx
+++ b/test/components/views/messages/MLocationBody-test.tsx
@@ -140,7 +140,9 @@ describe("MLocationBody", () => {
             });
 
             it("opens map dialog on click", () => {
-                const modalSpy = jest.spyOn(Modal, "createDialog").mockReturnValue(undefined);
+                const modalSpy = jest
+                    .spyOn(Modal, "createDialog")
+                    .mockReturnValue({ finished: new Promise(() => {}), close: jest.fn() });
                 const component = getComponent();
 
                 act(() => {
diff --git a/test/components/views/messages/MessageEvent-test.tsx b/test/components/views/messages/MessageEvent-test.tsx
index 6ec3d490e3..e8640415de 100644
--- a/test/components/views/messages/MessageEvent-test.tsx
+++ b/test/components/views/messages/MessageEvent-test.tsx
@@ -63,7 +63,7 @@ describe("MessageEvent", () => {
             event = mkEvent({
                 event: true,
                 type: VoiceBroadcastInfoEventType,
-                user: client.getUserId(),
+                user: client.getUserId()!,
                 room: room.roomId,
                 content: {
                     state: VoiceBroadcastInfoState.Started,
diff --git a/test/components/views/right_panel/PinnedMessagesCard-test.tsx b/test/components/views/right_panel/PinnedMessagesCard-test.tsx
index cf4dd61ec8..f9c2650b55 100644
--- a/test/components/views/right_panel/PinnedMessagesCard-test.tsx
+++ b/test/components/views/right_panel/PinnedMessagesCard-test.tsx
@@ -108,7 +108,7 @@ describe("<PinnedMessagesCard />", () => {
         const room = pins.props().room;
         const pinListener = mocked(room.currentState).on.mock.calls.find(
             ([eventName, listener]) => eventName === RoomStateEvent.Events,
-        )[1];
+        )![1];
 
         await act(async () => {
             // Emit the update
diff --git a/test/components/views/rooms/MemberList-test.tsx b/test/components/views/rooms/MemberList-test.tsx
index da6f27e582..735425c738 100644
--- a/test/components/views/rooms/MemberList-test.tsx
+++ b/test/components/views/rooms/MemberList-test.tsx
@@ -37,7 +37,7 @@ function generateRoomId() {
 
 describe("MemberList", () => {
     function createRoom(opts = {}) {
-        const room = new Room(generateRoomId(), null, client.getUserId());
+        const room = new Room(generateRoomId(), client, client.getUserId()!);
         if (opts) {
             Object.assign(room, opts);
         }
diff --git a/test/components/views/rooms/MessageComposer-test.tsx b/test/components/views/rooms/MessageComposer-test.tsx
index 3f445b244d..48feec7a8f 100644
--- a/test/components/views/rooms/MessageComposer-test.tsx
+++ b/test/components/views/rooms/MessageComposer-test.tsx
@@ -370,7 +370,7 @@ describe("MessageComposer", () => {
                 replyToEvent = mkEvent({
                     event: true,
                     type: EventType.RoomMessage,
-                    user: cli.getUserId(),
+                    user: cli.getUserId()!,
                     content: {},
                 });
 
diff --git a/test/components/views/rooms/RoomHeader-test.tsx b/test/components/views/rooms/RoomHeader-test.tsx
index 3aed3e6845..935745c761 100644
--- a/test/components/views/rooms/RoomHeader-test.tsx
+++ b/test/components/views/rooms/RoomHeader-test.tsx
@@ -377,7 +377,7 @@ describe("RoomHeader (React Testing Library)", () => {
                 content,
             });
             room.addLiveEvents([event]);
-            return { event_id: event.getId() };
+            return { event_id: event.getId()! };
         });
 
         alice = mkRoomMember(room.roomId, "@alice:example.org");
diff --git a/test/components/views/settings/KeyboardShortcut-test.tsx b/test/components/views/settings/KeyboardShortcut-test.tsx
index 2f9c94d752..614c2fd059 100644
--- a/test/components/views/settings/KeyboardShortcut-test.tsx
+++ b/test/components/views/settings/KeyboardShortcut-test.tsx
@@ -21,7 +21,7 @@ import { Key } from "../../../../src/Keyboard";
 import { mockPlatformPeg, unmockPlatformPeg } from "../../../test-utils/platform";
 import { KeyboardKey, KeyboardShortcut } from "../../../../src/components/views/settings/KeyboardShortcut";
 
-const renderKeyboardShortcut = (Component: React.FunctionComponentFactory<any>, props: Record<string, any>) => {
+const renderKeyboardShortcut = (Component: React.FunctionComponent<any>, props: Record<string, any>) => {
     return render(<Component {...props} />).container;
 };
 
diff --git a/test/components/views/settings/devices/DeviceDetails-test.tsx b/test/components/views/settings/devices/DeviceDetails-test.tsx
index a3b3c93e98..49173ffb5f 100644
--- a/test/components/views/settings/devices/DeviceDetails-test.tsx
+++ b/test/components/views/settings/devices/DeviceDetails-test.tsx
@@ -30,7 +30,6 @@ describe("<DeviceDetails />", () => {
     };
     const defaultProps: ComponentProps<typeof DeviceDetails> = {
         device: baseDevice,
-        pusher: null,
         isSigningOut: false,
         onSignOutDevice: jest.fn(),
         saveDeviceName: jest.fn(),
diff --git a/test/components/views/settings/devices/SelectableDeviceTile-test.tsx b/test/components/views/settings/devices/SelectableDeviceTile-test.tsx
index d9327d8ae4..b2e79fc70f 100644
--- a/test/components/views/settings/devices/SelectableDeviceTile-test.tsx
+++ b/test/components/views/settings/devices/SelectableDeviceTile-test.tsx
@@ -53,7 +53,7 @@ describe("<SelectableDeviceTile />", () => {
         const { container } = render(getComponent({ onSelect }));
 
         act(() => {
-            fireEvent.click(container.querySelector(`#device-tile-checkbox-${device.device_id}`));
+            fireEvent.click(container.querySelector(`#device-tile-checkbox-${device.device_id}`)!);
         });
 
         expect(onSelect).toHaveBeenCalled();
diff --git a/test/components/views/settings/devices/deleteDevices-test.tsx b/test/components/views/settings/devices/deleteDevices-test.tsx
index 743e0a5d54..80e62f423d 100644
--- a/test/components/views/settings/devices/deleteDevices-test.tsx
+++ b/test/components/views/settings/devices/deleteDevices-test.tsx
@@ -92,7 +92,7 @@ describe("deleteDevices()", () => {
         // opened modal
         expect(modalSpy).toHaveBeenCalled();
 
-        const [, { title, authData, aestheticsForStagePhases }] = modalSpy.mock.calls[0];
+        const { title, authData, aestheticsForStagePhases } = modalSpy.mock.calls[0][1]!;
 
         // modal opened as expected
         expect(title).toEqual("Authentication");
diff --git a/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx b/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
index 6356f652b3..cf2edb97e2 100644
--- a/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
+++ b/test/components/views/settings/tabs/user/SessionManagerTab-test.tsx
@@ -21,7 +21,7 @@ import { DeviceInfo } from "matrix-js-sdk/src/crypto/deviceinfo";
 import { logger } from "matrix-js-sdk/src/logger";
 import { DeviceTrustLevel } from "matrix-js-sdk/src/crypto/CrossSigning";
 import { VerificationRequest } from "matrix-js-sdk/src/crypto/verification/request/VerificationRequest";
-import { sleep } from "matrix-js-sdk/src/utils";
+import { defer, sleep } from "matrix-js-sdk/src/utils";
 import {
     ClientEvent,
     IMyDevice,
@@ -927,12 +927,9 @@ describe("<SessionManagerTab />", () => {
                 // get a handle for resolving the delete call
                 // because promise flushing after the confirm modal is resolving this too
                 // and we want to test the loading state here
-                let resolveDeleteRequest: (v?: IAuthData) => void;
+                const resolveDeleteRequest = defer<IAuthData>();
                 mockClient.deleteMultipleDevices.mockImplementation(() => {
-                    const promise = new Promise<IAuthData>((resolve) => {
-                        resolveDeleteRequest = resolve;
-                    });
-                    return promise;
+                    return resolveDeleteRequest.promise;
                 });
 
                 const { getByTestId } = render(getComponent());
@@ -972,7 +969,7 @@ describe("<SessionManagerTab />", () => {
                     undefined,
                 );
 
-                resolveDeleteRequest?.();
+                resolveDeleteRequest.resolve({});
             });
 
             it("signs out of all other devices from other sessions context menu", async () => {
diff --git a/test/editor/deserialize-test.ts b/test/editor/deserialize-test.ts
index bba9d6cd9f..bcc7de9a79 100644
--- a/test/editor/deserialize-test.ts
+++ b/test/editor/deserialize-test.ts
@@ -54,7 +54,7 @@ function textMessageReply(body: string, msgtype = "m.text") {
 function mergeAdjacentParts(parts: Part[]) {
     let prevPart: Part | undefined;
     for (let i = 0; i < parts.length; ++i) {
-        let part = parts[i];
+        let part: Part | undefined = parts[i];
         const isEmpty = !part.text.length;
         const isMerged = !isEmpty && prevPart && prevPart.merge?.(part);
         if (isEmpty || isMerged) {
diff --git a/test/editor/roundtrip-test.ts b/test/editor/roundtrip-test.ts
index b9a597b806..437c97e863 100644
--- a/test/editor/roundtrip-test.ts
+++ b/test/editor/roundtrip-test.ts
@@ -38,7 +38,7 @@ async function md2html(markdown: string): Promise<string> {
     const pc = createPartCreator();
     const oldModel = new EditorModel([], pc, () => {});
     await oldModel.update(markdown, "insertText", new DocumentOffset(markdown.length, false));
-    return htmlSerializeIfNeeded(oldModel, { forceHTML: true });
+    return htmlSerializeIfNeeded(oldModel, { forceHTML: true })!;
 }
 
 function html2md(html: string): string {
diff --git a/test/hooks/useProfileInfo-test.tsx b/test/hooks/useProfileInfo-test.tsx
index f9202de449..2619b7354d 100644
--- a/test/hooks/useProfileInfo-test.tsx
+++ b/test/hooks/useProfileInfo-test.tsx
@@ -143,7 +143,7 @@ describe("useProfileInfo", () => {
     });
 
     it("should be able to handle an empty result", async () => {
-        cli.getProfileInfo = () => null;
+        cli.getProfileInfo = () => null as unknown as Promise<{}>;
         const query = "@user:home.server";
 
         const wrapper = mount(
diff --git a/test/models/Call-test.ts b/test/models/Call-test.ts
index e825e5b1a4..2f01f06636 100644
--- a/test/models/Call-test.ts
+++ b/test/models/Call-test.ts
@@ -107,7 +107,7 @@ const setUpClientRoomAndStores = (): {
             content,
         });
         room.addLiveEvents([event]);
-        return { event_id: event.getId() };
+        return { event_id: event.getId()! };
     });
 
     setupAsyncStoreWithClient(WidgetStore.instance, client);
diff --git a/test/modules/AppModule-test.ts b/test/modules/AppModule-test.ts
index 6fdf16d694..178487a91d 100644
--- a/test/modules/AppModule-test.ts
+++ b/test/modules/AppModule-test.ts
@@ -20,7 +20,7 @@ import { AppModule } from "../../src/modules/AppModule";
 describe("AppModule", () => {
     describe("constructor", () => {
         it("should call the factory immediately", () => {
-            let module: MockModule;
+            let module: MockModule | undefined;
             const appModule = new AppModule((api) => {
                 if (module) {
                     throw new Error("State machine error: Factory called twice");
diff --git a/test/modules/MockModule.ts b/test/modules/MockModule.ts
index b4b905fcbf..ab29b02508 100644
--- a/test/modules/MockModule.ts
+++ b/test/modules/MockModule.ts
@@ -30,7 +30,7 @@ export class MockModule extends RuntimeModule {
 }
 
 export function registerMockModule(): MockModule {
-    let module: MockModule;
+    let module: MockModule | undefined;
     ModuleRunner.instance.registerModule((api) => {
         if (module) {
             throw new Error("State machine error: ModuleRunner created the module twice");
diff --git a/test/stores/SpaceStore-test.ts b/test/stores/SpaceStore-test.ts
index 6354b5bfa1..1b9ae8da60 100644
--- a/test/stores/SpaceStore-test.ts
+++ b/test/stores/SpaceStore-test.ts
@@ -800,7 +800,7 @@ describe("SpaceStore", () => {
                     testUtils.mockStateEventImplementation([childEvent]),
                 );
 
-                client.emit(RoomStateEvent.Events, childEvent, spaceRoom.currentState, undefined);
+                client.emit(RoomStateEvent.Events, childEvent, spaceRoom.currentState, null);
             };
 
             const addMember = (spaceId: string, user: RoomMember) => {
@@ -964,7 +964,7 @@ describe("SpaceStore", () => {
                 }
             });
 
-            client.emit(RoomStateEvent.Members, event, null, null);
+            client.emit(RoomStateEvent.Members, event, space.currentState, dm1Partner);
             return deferred.resolve(true) as unknown as Promise<boolean>;
         });
 
@@ -1279,7 +1279,7 @@ describe("SpaceStore", () => {
             user: dm1Partner.userId,
             room: space1,
         });
-        client.emit(RoomStateEvent.Members, memberEvent, undefined, undefined);
+        client.emit(RoomStateEvent.Members, memberEvent, rootSpace.currentState, dm1Partner);
         jest.runOnlyPendingTimers();
         expect(SpaceStore.instance.getSpaceFilteredUserIds(space1).has(dm1Partner.userId)).toBeTruthy();
         const dm1Room = mkRoom(dm1);
diff --git a/test/stores/VoiceRecordingStore-test.ts b/test/stores/VoiceRecordingStore-test.ts
index 22695081ad..66eeb81103 100644
--- a/test/stores/VoiceRecordingStore-test.ts
+++ b/test/stores/VoiceRecordingStore-test.ts
@@ -21,7 +21,7 @@ import { MatrixClientPeg } from "../../src/MatrixClientPeg";
 import { flushPromises } from "../test-utils";
 import { VoiceMessageRecording } from "../../src/audio/VoiceMessageRecording";
 
-const stubClient = {} as undefined as MatrixClient;
+const stubClient = {} as unknown as MatrixClient;
 jest.spyOn(MatrixClientPeg, "get").mockReturnValue(stubClient);
 
 describe("VoiceRecordingStore", () => {
diff --git a/test/stores/room-list/RoomListStore-test.ts b/test/stores/room-list/RoomListStore-test.ts
index e0ee766f91..5c6435780e 100644
--- a/test/stores/room-list/RoomListStore-test.ts
+++ b/test/stores/room-list/RoomListStore-test.ts
@@ -216,7 +216,7 @@ describe("RoomListStore", () => {
 
         // But when we update the feature flag
         featureFlagValue = true;
-        watchCallback(
+        watchCallback!(
             "feature_dynamic_room_predecessors",
             "",
             SettingLevel.DEFAULT,
diff --git a/test/stores/room-list/algorithms/RecentAlgorithm-test.ts b/test/stores/room-list/algorithms/RecentAlgorithm-test.ts
index 0375065e94..d86fe9e775 100644
--- a/test/stores/room-list/algorithms/RecentAlgorithm-test.ts
+++ b/test/stores/room-list/algorithms/RecentAlgorithm-test.ts
@@ -68,6 +68,7 @@ describe("RecentAlgorithm", () => {
 
         it("returns a fake ts for rooms without a timeline", () => {
             const room = mkRoom(cli, "!new:example.org");
+            // @ts-ignore
             room.timeline = undefined;
             expect(algorithm.getLastTs(room, "@john:matrix.org")).toBe(Number.MAX_SAFE_INTEGER);
         });
diff --git a/test/utils/beacon/geolocation-test.ts b/test/utils/beacon/geolocation-test.ts
index 688e92ba70..0f9aba483f 100644
--- a/test/utils/beacon/geolocation-test.ts
+++ b/test/utils/beacon/geolocation-test.ts
@@ -196,7 +196,7 @@ describe("geolocation utilities", () => {
             // suppress expected errors from test log
             jest.spyOn(logger, "error").mockImplementation(() => {});
             geolocation.watchPosition.mockImplementation((_callback, error) => {
-                error(getMockGeolocationPositionError(1, "message"));
+                error!(getMockGeolocationPositionError(1, "message"));
                 return -1;
             });
             const positionHandler = jest.fn();
@@ -224,7 +224,7 @@ describe("geolocation utilities", () => {
             jest.spyOn(logger, "error").mockImplementation(() => {});
 
             const timeoutError = getMockGeolocationPositionError(3, "message");
-            geolocation.getCurrentPosition.mockImplementation((callback, error) => error(timeoutError));
+            geolocation.getCurrentPosition.mockImplementation((callback, error) => error!(timeoutError));
 
             await expect(() => getCurrentPosition()).rejects.toThrow(GeolocationError.Timeout);
         });
diff --git a/test/voice-broadcast/models/VoiceBroadcastRecording-test.ts b/test/voice-broadcast/models/VoiceBroadcastRecording-test.ts
index 3cf71a7a94..312ee7f785 100644
--- a/test/voice-broadcast/models/VoiceBroadcastRecording-test.ts
+++ b/test/voice-broadcast/models/VoiceBroadcastRecording-test.ts
@@ -135,7 +135,7 @@ describe("VoiceBroadcastRecording", () => {
                         event_id: infoEvent.getId(),
                     },
                 } as VoiceBroadcastInfoEventContent,
-                client.getUserId(),
+                client.getUserId()!,
             );
         });
     };
diff --git a/test/voice-broadcast/stores/VoiceBroadcastRecordingsStore-test.ts b/test/voice-broadcast/stores/VoiceBroadcastRecordingsStore-test.ts
index 2d1126603c..ff7a50aef3 100644
--- a/test/voice-broadcast/stores/VoiceBroadcastRecordingsStore-test.ts
+++ b/test/voice-broadcast/stores/VoiceBroadcastRecordingsStore-test.ts
@@ -49,14 +49,14 @@ describe("VoiceBroadcastRecordingsStore", () => {
         infoEvent = mkVoiceBroadcastInfoStateEvent(
             roomId,
             VoiceBroadcastInfoState.Started,
-            client.getUserId(),
-            client.getDeviceId(),
+            client.getUserId()!,
+            client.getDeviceId()!,
         );
         otherInfoEvent = mkVoiceBroadcastInfoStateEvent(
             roomId,
             VoiceBroadcastInfoState.Started,
-            client.getUserId(),
-            client.getDeviceId(),
+            client.getUserId()!,
+            client.getDeviceId()!,
         );
         recording = new VoiceBroadcastRecording(infoEvent, client);
         otherRecording = new VoiceBroadcastRecording(otherInfoEvent, client);
diff --git a/test/voice-broadcast/utils/VoiceBroadcastResumer-test.ts b/test/voice-broadcast/utils/VoiceBroadcastResumer-test.ts
index b166bbb9bd..7c07554fd2 100644
--- a/test/voice-broadcast/utils/VoiceBroadcastResumer-test.ts
+++ b/test/voice-broadcast/utils/VoiceBroadcastResumer-test.ts
@@ -54,7 +54,7 @@ describe("VoiceBroadcastResumer", () => {
                         event_id: startedInfoEvent.getId(),
                     },
                 } as VoiceBroadcastInfoEventContent,
-                client.getUserId(),
+                client.getUserId()!,
             );
         });
     };
diff --git a/test/voice-broadcast/utils/startNewVoiceBroadcastRecording-test.ts b/test/voice-broadcast/utils/startNewVoiceBroadcastRecording-test.ts
index 5f2447d858..e417e7e0fd 100644
--- a/test/voice-broadcast/utils/startNewVoiceBroadcastRecording-test.ts
+++ b/test/voice-broadcast/utils/startNewVoiceBroadcastRecording-test.ts
@@ -161,7 +161,7 @@ describe("startNewVoiceBroadcastRecording", () => {
                         device_id: client.getDeviceId(),
                         state: VoiceBroadcastInfoState.Started,
                     },
-                    client.getUserId(),
+                    client.getUserId()!,
                 );
                 expect(recording!.infoEvent).toBe(infoEvent);
                 expect(recording!.start).toHaveBeenCalled();