Add a warning

src/i18n/strings/en_EN.json

@@ -3084,6 +3084,7 @@
             "enable_fallback_ice_server": "Allow fallback call assist server (%(server)s)",
             "enable_fallback_ice_server_description": "Only applies if your homeserver does not offer one. Your IP address would be shared during a call.",
             "mirror_local_feed": "Mirror local video feed",
+            "mirror_local_feed_description": "Not supported when using Element Call",
             "missing_permissions_prompt": "Missing media permissions, click the button below to request.",
             "noise_suppression": "Noise suppression",
             "request_permissions": "Request media permissions",

src/settings/Settings.tsx

@@ -941,6 +941,7 @@ export const SETTINGS: Settings = {
     "VideoView.flipVideoHorizontally": {
         supportedLevels: LEVELS_ACCOUNT_SETTINGS,
         displayName: _td("settings|voip|mirror_local_feed"),
+        description: _td("settings|voip|mirror_local_feed_description"),
         default: true,
     },
     "theme": {