Mine does the same now after update, so annoying. I really don't want to have to factory reset as now the geniuses at Samsung have decided to not support memory cards anymore I will lose all my music and files etc. At least with a memory card you could put it all on there then take it out and factory reset then just pop the card back in. If this auto rotate fixes for you can you let me know on here and I will do the same for you?
I've had a few problems I've got a s21 ultra absolutely should have no problems with it for how !uch Samsung charge for the phone. Real let down. At least with 2 of us with this problem it seems like a software problem rather than the actual phone
This is quite unusual behaviour that I haven't seen before. If you launch a video from the native video-player (for example, using My Files), does it revert back to portrait as well after "X" amount of minutes?