I hope this has not been posted already, couldn't find a post relating to mobile apps.
I have an unread chat notification on my Teams Mobile app which I am unable to get away after trying all the suggested solutions, uninstalling the app, switching off all notifications, clicking on all chats, but I have not been successful. The mobile app also doesn't have an unread filtering option.
I don't have unread notifications on the desktop app.
Whenever this happens to me, it's usually some chat I've participated in which is now flagged as unread for whatever reason. The only solution I've found so far is to go over the list of chats and click on those that are marked as having new activity... not really a solution :\