I bought S21 Ultra last October and I regret it so.
1: The sound volume is very bad.
2: The phone will only charge when I turn it on airplane mode.
3: This week my pictures where not working, got it back to work after complete reboot.
I am using now my S9 more than that horrible S21 ultra.
4: Today I made some nice videos and now I was showing it to someone and there is ony sound and the video is freezing.
Backup your device and try resetting it and while you're at it clear the system cache in Recovery Mode.
After restarting the device and letting everything update THEN go through the above list and verify whether they've either been solved or they continue to be an issue.
Have you consistently updated your device every month? Have you dropped your device, had it been dunked in water? Supply more information please