Autoplay muted doesn't show a notification because we check if the playback is in the "autoplay muted" state which is defined by the playback being autoplayed, currently muted and not allowed to play otherwise. The last bit is not true on websites running in a Web APK with their origin whitelisted.

An alternative would be to consider autoplay muted anything that is autoplaying and muted regardless of the locking. Though, this might have side effect and false positive which is the reason why it was not done in the first place.