Same problem here, been searching all over the internet for a solution and nothing seems to help. Even tried locking the phone on portrait and the same thing happens as soon as I use an full screen app.
This happened to me for 2 days just last week but it automatically fixed. It doesn't happen anymore. I don't know what fixed it. There is no solution to it I think. Because it is a software bug. So, only a software update can fix this, not playing around with settings.
First there is no solution to the problem from Samsung. They need to fix this including gaming fps/lag.
But there is a temporary solution.
I have noticed that wallpaper glitch happens to wallpapers applied from Galaxy Themes only. So, you should apply a wallpaper from the Gallery. This will temporarily fix the issue. I have done same with my Note 10. I saved a wallpaper in my Gallery and then pulled it from gallery while applying it. And it doesn't rotate anymore. So, don't apply Samsung's own wallpaper either default or from Galaxy Themes.