Good!
Immediately take a system backup:
This is not Windows: 5.9 is an EOL kernel: it will be removed in one of the next upgrades, so better upgrade now.
5.4 has been an LTS kernel since a while and 5.10 is an LTS kernel since very little time.
so for rock stable performance, take 5.4 until 5.10 has reached the stability of 5.4.
That being said, if 5.9 works, don’t delete it, but keep it around and install both 5.4 and 5.10 on top of 5.9 and boot them and try things out on all 3 of them.
P.S. Now you have a stable system, don’t install anything weird (I don’t even know which screen saver you’ve installed, so can’t give you any guidance…)
P.PS. please confirm your OS itself works now.