I bought new A31 few days ago and facing the same issue. Last software update was 22 Aug 2020, that's 1st July 2020 patch. So, Samsung haven't fixed it and new models are also launched with the same problem. Seriously, just put the fingerprint s...

The in-display fingerprint sensor is making this issue. When you turn off the fingerprint lock, the wallpaper will appear in real quality.

I'm also facing this issue on Samsung A31. Very disappointed. I hope I can find the solution of this problem.