im having the same issue. Same with most apps, either cutting the top or the bottom. Its driving me insane! S20
dont want to sound condescending - but for the apps you're having issues with - have you tried going into
full screen apps
change under the problematic app - from auto to - full screen
then try again see if it works
I had this with a couple of apps on my Ultra but it didn't last long and they went back to normal. It never happened with Facebook though. One thing I did notice is that the apps it happened on are ones I'd transferred over using Smart Switch, so I wonder if they'd retained some window size settings from the previous phone. I don't know if you've already tried this but it might be worth wiping the data for the app then reinstalling it (although that may not be necessary). So I think try this:
1. Go to the app info (in the Apps settings), then go into "Storage" and hit "Clear Cache". Start the app up again
2. If that doesn't work, do the same as 1. but hit "Clear Data" instead (note: this will wipe all Facebook data on your phone and require you to sign in again). Start the app up again
3. If that still doesn't work, try uninstalling and reinstalling the app..
I had the same issue with my S20 Ultra and tried everything suggested above several times. Then I realised the only I'm doing with the S20 Ultra that I didn't do with my S10 is using Dark mode all the time. So I turned of Dark mode and Facebook looked normal again. Even after switching back to Dark it's functioning fine.