diff --git a/src/ClientContext.tsx b/src/ClientContext.tsx
index 3c99c04d..619626f7 100644
--- a/src/ClientContext.tsx
+++ b/src/ClientContext.tsx
@@ -317,7 +317,7 @@ export const ClientProvider: FC<Props> = ({ children }) => {
       initClientState.client.on(ClientEvent.Sync, onSync);
     }
 
-    return () => {
+    return (): void => {
       if (initClientState.client) {
         initClientState.client.removeListener(ClientEvent.Sync, onSync);
       }
diff --git a/src/Toast.tsx b/src/Toast.tsx
index ca3e2fab..fffbec97 100644
--- a/src/Toast.tsx
+++ b/src/Toast.tsx
@@ -76,7 +76,7 @@ export const Toast: FC<Props> = ({
   useEffect(() => {
     if (open && autoDismiss !== undefined) {
       const timeout = setTimeout(onDismiss, autoDismiss);
-      return () => clearTimeout(timeout);
+      return (): void => clearTimeout(timeout);
     }
   }, [open, autoDismiss, onDismiss]);
 
diff --git a/src/auth/useInteractiveLogin.ts b/src/auth/useInteractiveLogin.ts
index 83767f51..7ea01811 100644
--- a/src/auth/useInteractiveLogin.ts
+++ b/src/auth/useInteractiveLogin.ts
@@ -16,7 +16,11 @@ limitations under the License.
 
 import { useCallback } from "react";
 import { InteractiveAuth } from "matrix-js-sdk/src/interactive-auth";
-import { createClient, MatrixClient } from "matrix-js-sdk/src/matrix";
+import {
+  createClient,
+  LoginResponse,
+  MatrixClient,
+} from "matrix-js-sdk/src/matrix";
 
 import { initClient } from "../matrix-utils";
 import { Session } from "../ClientContext";
@@ -37,7 +41,7 @@ export function useInteractiveLogin(): (
 
     const interactiveAuth = new InteractiveAuth({
       matrixClient: authClient,
-      doRequest: () =>
+      doRequest: (): Promise<LoginResponse> =>
         authClient.login("m.login.password", {
           identifier: {
             type: "m.id.user",
diff --git a/src/auth/useInteractiveRegistration.ts b/src/auth/useInteractiveRegistration.ts
index 135d1fac..f7a7854e 100644
--- a/src/auth/useInteractiveRegistration.ts
+++ b/src/auth/useInteractiveRegistration.ts
@@ -16,7 +16,11 @@ limitations under the License.
 
 import { useState, useEffect, useCallback, useRef } from "react";
 import { InteractiveAuth } from "matrix-js-sdk/src/interactive-auth";
-import { createClient, MatrixClient } from "matrix-js-sdk/src/matrix";
+import {
+  createClient,
+  MatrixClient,
+  RegisterResponse,
+} from "matrix-js-sdk/src/matrix";
 
 import { initClient } from "../matrix-utils";
 import { Session } from "../ClientContext";
@@ -69,7 +73,7 @@ export const useInteractiveRegistration = (): {
     ): Promise<[MatrixClient, Session]> => {
       const interactiveAuth = new InteractiveAuth({
         matrixClient: authClient.current!,
-        doRequest: (auth) =>
+        doRequest: (auth): Promise<RegisterResponse> =>
           authClient.current!.registerRequest({
             username,
             password,
diff --git a/src/home/useGroupCallRooms.ts b/src/home/useGroupCallRooms.ts
index 21426a2d..ea513587 100644
--- a/src/home/useGroupCallRooms.ts
+++ b/src/home/useGroupCallRooms.ts
@@ -166,7 +166,7 @@ export function useGroupCallRooms(client: MatrixClient): GroupCallRoom[] {
       updateRooms,
     );
     client.on(RoomEvent.MyMembership, updateRooms);
-    return () => {
+    return (): void => {
       client.matrixRTC.off(
         MatrixRTCSessionManagerEvents.SessionStarted,
         updateRooms,
diff --git a/src/livekit/MediaDevicesContext.tsx b/src/livekit/MediaDevicesContext.tsx
index 027f12ae..b42a0afa 100644
--- a/src/livekit/MediaDevicesContext.tsx
+++ b/src/livekit/MediaDevicesContext.tsx
@@ -59,7 +59,7 @@ function useObservableState<T>(
     // observable state doesn't run in SSR
     if (typeof window === "undefined" || !observable) return;
     const subscription = observable.subscribe(setState);
-    return () => subscription.unsubscribe();
+    return (): void => subscription.unsubscribe();
   }, [observable]);
   return state;
 }
diff --git a/src/livekit/useECConnectionState.ts b/src/livekit/useECConnectionState.ts
index ae9160b1..c2bd0aa7 100644
--- a/src/livekit/useECConnectionState.ts
+++ b/src/livekit/useECConnectionState.ts
@@ -192,7 +192,7 @@ export function useECConnectionState(
       livekitRoom.on(RoomEvent.ConnectionStateChanged, onConnStateChanged);
     }
 
-    return () => {
+    return (): void => {
       if (oldRoom)
         oldRoom.off(RoomEvent.ConnectionStateChanged, onConnStateChanged);
     };
diff --git a/src/profile/useProfile.ts b/src/profile/useProfile.ts
index eba0420f..ab72a9bf 100644
--- a/src/profile/useProfile.ts
+++ b/src/profile/useProfile.ts
@@ -82,7 +82,7 @@ export function useProfile(client: MatrixClient | undefined): UseProfile {
       user?.on(UserEvent.AvatarUrl, onChangeUser);
     }
 
-    return () => {
+    return (): void => {
       if (user) {
         user.removeListener(UserEvent.DisplayName, onChangeUser);
         user.removeListener(UserEvent.AvatarUrl, onChangeUser);
diff --git a/src/room/GroupCallView.tsx b/src/room/GroupCallView.tsx
index a3fe1dbd..2052a649 100644
--- a/src/room/GroupCallView.tsx
+++ b/src/room/GroupCallView.tsx
@@ -94,7 +94,7 @@ export const GroupCallView: FC<Props> = ({
 
   useEffect(() => {
     window.rtcSession = rtcSession;
-    return () => {
+    return (): void => {
       delete window.rtcSession;
     };
   }, [rtcSession]);
@@ -200,7 +200,7 @@ export const GroupCallView: FC<Props> = ({
         await widget!.api.transport.reply(ev.detail, {});
       };
       widget.lazyActions.on(ElementWidgetActions.JoinCall, onJoin);
-      return () => {
+      return (): void => {
         widget!.lazyActions.off(ElementWidgetActions.JoinCall, onJoin);
       };
     } else if (widget && !preload && skipLobby) {
@@ -255,7 +255,7 @@ export const GroupCallView: FC<Props> = ({
         await leaveRTCSession(rtcSession);
       };
       widget.lazyActions.once(ElementWidgetActions.HangupCall, onHangup);
-      return () => {
+      return (): void => {
         widget!.lazyActions.off(ElementWidgetActions.HangupCall, onHangup);
       };
     }
diff --git a/src/room/InCallView.tsx b/src/room/InCallView.tsx
index 56cdba49..94edace7 100644
--- a/src/room/InCallView.tsx
+++ b/src/room/InCallView.tsx
@@ -97,7 +97,7 @@ export const ActiveCall: FC<ActiveCallProps> = (props) => {
   );
 
   useEffect(() => {
-    return () => {
+    return (): void => {
       livekitRoom?.disconnect();
     };
     // eslint-disable-next-line react-hooks/exhaustive-deps
@@ -220,7 +220,7 @@ export const InCallView: FC<InCallViewProps> = subscribe(
           onSpotlightLayout,
         );
 
-        return () => {
+        return (): void => {
           widget!.lazyActions.off(
             ElementWidgetActions.TileLayout,
             onTileLayout,
diff --git a/src/room/VideoPreview.tsx b/src/room/VideoPreview.tsx
index 49342c42..2f6dbbbc 100644
--- a/src/room/VideoPreview.tsx
+++ b/src/room/VideoPreview.tsx
@@ -110,7 +110,7 @@ export const VideoPreview: FC<Props> = ({
     if (videoEl.current) {
       videoTrack?.attach(videoEl.current);
     }
-    return () => {
+    return (): void => {
       videoTrack?.detach();
     };
   }, [videoTrack]);
diff --git a/src/room/useActiveFocus.ts b/src/room/useActiveFocus.ts
index 8e6435d2..5a7b1743 100644
--- a/src/room/useActiveFocus.ts
+++ b/src/room/useActiveFocus.ts
@@ -64,7 +64,7 @@ export function useActiveFocus(
       onMembershipsChanged,
     );
 
-    return () => {
+    return (): void => {
       rtcSession.off(
         MatrixRTCSessionEvent.MembershipsChanged,
         onMembershipsChanged,
diff --git a/src/room/usePageUnload.ts b/src/room/usePageUnload.ts
index 6af3a8f9..679ae9e9 100644
--- a/src/room/usePageUnload.ts
+++ b/src/room/usePageUnload.ts
@@ -50,7 +50,7 @@ export function usePageUnload(callback: () => void): void {
     // @ts-ignore
     window.addEventListener("beforeunload", onBeforeUnload);
 
-    return () => {
+    return (): void => {
       window.removeEventListener("pagehide", onBeforeUnload);
       // eslint-disable-next-line @typescript-eslint/ban-ts-comment
       // @ts-ignore
diff --git a/src/settings/ProfileSettingsTab.tsx b/src/settings/ProfileSettingsTab.tsx
index 83ecae74..e0062f58 100644
--- a/src/settings/ProfileSettingsTab.tsx
+++ b/src/settings/ProfileSettingsTab.tsx
@@ -47,7 +47,7 @@ export const ProfileSettingsTab: FC<Props> = ({ client }) => {
   useEffect(() => {
     const form = formRef.current!;
     // Auto-save when the user dismisses this component
-    return () => {
+    return (): void => {
       if (formChanged.current) {
         const data = new FormData(form);
         const displayNameDataEntry = data.get("displayName");
diff --git a/src/settings/submit-rageshake.ts b/src/settings/submit-rageshake.ts
index 675314bc..3a98b831 100644
--- a/src/settings/submit-rageshake.ts
+++ b/src/settings/submit-rageshake.ts
@@ -334,7 +334,7 @@ export function useRageshakeRequestModal(
 
     client.on(ClientEvent.Event, onEvent);
 
-    return () => {
+    return (): void => {
       client.removeListener(ClientEvent.Event, onEvent);
     };
   }, [setOpen, roomId, client]);
diff --git a/src/useEvents.ts b/src/useEvents.ts
index a116a050..66c5084a 100644
--- a/src/useEvents.ts
+++ b/src/useEvents.ts
@@ -33,7 +33,7 @@ export function useEventTarget<T extends Event>(
   useEffect(() => {
     if (target) {
       target.addEventListener(eventType, listener as EventListener, options);
-      return () =>
+      return (): void =>
         target.removeEventListener(
           eventType,
           listener as EventListener,
@@ -55,7 +55,7 @@ export function useTypedEventEmitter<
 ): void {
   useEffect(() => {
     emitter.on(eventType, listener);
-    return () => {
+    return (): void => {
       emitter.off(eventType, listener);
     };
   }, [emitter, eventType, listener]);
@@ -72,7 +72,7 @@ export function useEventEmitterThree<
 ): void {
   useEffect(() => {
     emitter.on(eventType, listener);
-    return () => {
+    return (): void => {
       emitter.off(eventType, listener);
     };
   }, [emitter, eventType, listener]);
diff --git a/src/useLocalStorage.ts b/src/useLocalStorage.ts
index 07d487ea..318c691f 100644
--- a/src/useLocalStorage.ts
+++ b/src/useLocalStorage.ts
@@ -32,7 +32,7 @@ export const useLocalStorage = (
 
   useEffect(() => {
     localStorageBus.on(key, setValue);
-    return () => {
+    return (): void => {
       localStorageBus.off(key, setValue);
     };
   }, [key, setValue]);
diff --git a/src/useLocationNavigation.ts b/src/useLocationNavigation.ts
index 08f28fc9..cc1c2f9f 100644
--- a/src/useLocationNavigation.ts
+++ b/src/useLocationNavigation.ts
@@ -34,7 +34,7 @@ export function useLocationNavigation(enabled = false): void {
       });
     }
 
-    return () => {
+    return (): void => {
       // eslint-disable-next-line @typescript-eslint/ban-ts-comment
       // @ts-ignore
       if (unblock) {
diff --git a/src/useMatrixRTCSessionJoinState.ts b/src/useMatrixRTCSessionJoinState.ts
index 7aac4e83..af7618df 100644
--- a/src/useMatrixRTCSessionJoinState.ts
+++ b/src/useMatrixRTCSessionJoinState.ts
@@ -38,7 +38,7 @@ export function useMatrixRTCSessionJoinState(
   useEffect(() => {
     rtcSession.on(MatrixRTCSessionEvent.JoinStateChanged, onJoinStateChanged);
 
-    return () => {
+    return (): void => {
       rtcSession.off(
         MatrixRTCSessionEvent.JoinStateChanged,
         onJoinStateChanged,
diff --git a/src/useMatrixRTCSessionMemberships.ts b/src/useMatrixRTCSessionMemberships.ts
index 3873b7a2..a7d62ba7 100644
--- a/src/useMatrixRTCSessionMemberships.ts
+++ b/src/useMatrixRTCSessionMemberships.ts
@@ -40,7 +40,7 @@ export function useMatrixRTCSessionMemberships(
       onMembershipsChanged,
     );
 
-    return () => {
+    return (): void => {
       rtcSession.off(
         MatrixRTCSessionEvent.MembershipsChanged,
         onMembershipsChanged,
diff --git a/src/useWakeLock.ts b/src/useWakeLock.ts
index 5f931f75..b1174fa1 100644
--- a/src/useWakeLock.ts
+++ b/src/useWakeLock.ts
@@ -47,7 +47,7 @@ export function useWakeLock(): void {
       onVisiblityChange();
       document.addEventListener("visiblitychange", onVisiblityChange);
 
-      return () => {
+      return (): void => {
         mounted = false;
         if (lock !== null)
           lock
diff --git a/src/video-grid/NewVideoGrid.tsx b/src/video-grid/NewVideoGrid.tsx
index 6de5f58d..61813125 100644
--- a/src/video-grid/NewVideoGrid.tsx
+++ b/src/video-grid/NewVideoGrid.tsx
@@ -33,6 +33,7 @@ import {
   VideoGridProps as Props,
   TileSpring,
   ChildrenProperties,
+  TileSpringUpdate,
 } from "./VideoGrid";
 import { useReactiveState } from "../useReactiveState";
 import { useMergedRefs } from "../useMergedRefs";
@@ -110,7 +111,7 @@ export function NewVideoGrid<T>({
       });
 
       observer.observe(slotsRoot, { attributes: true });
-      return () => observer.disconnect();
+      return (): void => observer.disconnect();
     }
   }, [slotsRoot, setRenderedGeneration]);
 
@@ -174,8 +175,8 @@ export function NewVideoGrid<T>({
   const [tileTransitions, springRef] = useTransition(
     tiles,
     () => ({
-      key: ({ item }: Tile<T>) => item.id,
-      from: ({ x, y, width, height }: Tile<T>) => ({
+      key: ({ item }: Tile<T>): string => item.id,
+      from: ({ x, y, width, height }: Tile<T>): TileSpringUpdate => ({
         opacity: 0,
         scale: 0,
         shadow: 0,
@@ -188,7 +189,13 @@ export function NewVideoGrid<T>({
         immediate: disableAnimations,
       }),
       enter: { opacity: 1, scale: 1, immediate: disableAnimations },
-      update: ({ item, x, y, width, height }: Tile<T>) =>
+      update: ({
+        item,
+        x,
+        y,
+        width,
+        height,
+      }: Tile<T>): TileSpringUpdate | null =>
         item.id === dragState.current?.tileId
           ? null
           : {
@@ -230,7 +237,7 @@ export function NewVideoGrid<T>({
                 disableAnimations || ((key): boolean => key === "zIndex"),
               // Allow the tile's position to settle before pushing its
               // z-index back down
-              delay: (key) => (key === "zIndex" ? 500 : 0),
+              delay: (key): number => (key === "zIndex" ? 500 : 0),
             }
           : {
               scale: 1.1,
diff --git a/src/video-grid/VideoGrid.tsx b/src/video-grid/VideoGrid.tsx
index 202539ba..fa56bd88 100644
--- a/src/video-grid/VideoGrid.tsx
+++ b/src/video-grid/VideoGrid.tsx
@@ -77,6 +77,13 @@ export interface TileSpring {
   height: number;
 }
 
+export interface TileSpringUpdate extends Partial<TileSpring> {
+  from?: Partial<TileSpring>;
+  reset?: boolean;
+  immediate?: boolean | ((key: string) => boolean);
+  delay?: (key: string) => number;
+}
+
 type LayoutDirection = "vertical" | "horizontal";
 
 export function useVideoGridLayout(hasScreenshareFeeds: boolean): {
@@ -120,7 +127,7 @@ function useIsMounted(): MutableRefObject<boolean> {
   useEffect(() => {
     isMountedRef.current = true;
 
-    return () => {
+    return (): void => {
       isMountedRef.current = false;
     };
   }, []);
@@ -1026,7 +1033,7 @@ export function VideoGrid<T>({
       const oneOnOneLayout =
         tiles.length === 2 && !tiles.some((t) => t.focused);
 
-      return (tileIndex: number) => {
+      return (tileIndex: number): TileSpringUpdate => {
         const tile = tiles[tileIndex];
         const tilePosition = tilePositions[tile.order];
         const draggingTile = draggingTileRef.current;
@@ -1045,7 +1052,7 @@ export function VideoGrid<T>({
             zIndex: 2,
             shadow: 15,
             shadowSpread: 0,
-            immediate: (key: string) =>
+            immediate: (key: string): boolean =>
               disableAnimations ||
               key === "zIndex" ||
               key === "x" ||
@@ -1112,14 +1119,14 @@ export function VideoGrid<T>({
             shadowSpread: oneOnOneLayout && tile.item.local ? 1 : 0,
             from,
             reset,
-            immediate: (key: string) =>
+            immediate: (key: string): boolean =>
               disableAnimations ||
               key === "zIndex" ||
               key === "shadow" ||
               key === "shadowSpread",
             // If we just stopped dragging a tile, give it time for the
             // animation to settle before pushing its z-index back down
-            delay: (key: string) => (key === "zIndex" ? 500 : 0),
+            delay: (key: string): number => (key === "zIndex" ? 500 : 0),
           };
         }
       };