I have now tried to solve this issue for about 4 weeks since getting my 15 Pro Max.
My Messenger app shows one new message on the icon (red dot with a ”1”). So then I go into that message and read/answer it.
If I then minimize the app to do something else Messenger will continue to show 1 new message on the icon. The only way to get rid of the notification is to go back out of that specific chat that caused the notification to the main screen where I see all my conversations. Then the app badge notification will disappear.
So far I have tried reinstalling the app, turning notifications on/off, tried different notification settings, updated the app, and rebooted the phone.
Had an old Samsung S9 plus before this with zero issues like this one.
Any help would be greatly appreciated, tried to Google this but can’t find any issue that is like the above.