Hello and welcome to the forum,
This problem was plaguing some Linux users since Krita 5 Beta (I believe), but it was fixed this week by the amazing @dkazakov. You can see the details in the post I linked bellow.
Krita 5.0 is EXTREMELY unstable, constant crashes
You can use the Krita plus version until the next stable realease comes out, since those already has the fix.
Cheers.