There is no Ubuntu 21 release, so please be exact in future.
Assuming it's 21.04, I'd look for clues in /var/crash/ (ie. is there a crash file).
If a crash file is present, please submit the bug report (it'll contain useful details in finding a bug if one is found, or even for us to get clues). To submit the bug use
Code:
ubuntu-bug /var/crash/[filename].crash
where you'll need to replace [filename] with the correct name, and thank you for helping to test Ubuntu 21.04, and helping to make it better on it's release.