SUMMARY
Krita segfaulted when using basic tools, like paintbrushes. I dont remember the exact action I was doing at the moment of the crash, but I included the report from coredumpctl.
Not sure if this is enough for you, to be able to fix it tho.

OBSERVED RESULT
App randomly closes, because of a segfault.


SOFTWARE/OS VERSIONS
Krita 5.0.0 appimage
Linux Mint based on Ubuntu 20.04

ADDITIONAL INFORMATION: output of coredumpctl

coredumpctl gdb 1188734
           PID: 1188734 (AppRun)
           UID: 1000 (gergely)
           GID: 1000 (gergely)
        Signal: 11 (SEGV)
     Timestamp: Mon 2021-12-27 00:23:33 CET (14h ago)
  Command Line: .local/bin/krita-5.0.0-x86_64.appimage
    Executable: /tmp/.mount_krita-zVUO7G/usr/bin/krita
 Control Group: /user.slice/user-1000.slice/session-c2.scope
          Unit: session-c2.scope
         Slice: user-1000.slice
       Session: c2
     Owner UID: 1000 (gergely)
       Boot ID: 32bf596775494185a5fcbadc20e0321d
    Machine ID: 61f22c5f670f40d78231ac18132213cb
      Hostname: gmint
       Storage: /var/lib/systemd/coredump/core.AppRun.1000.32bf596775494185a5fcbadc20e0321d.1188734.1640561013000000000000.lz4
       Message: Process 1188734 (AppRun) of user 1000 dumped core.
                
                Stack trace of thread 1188734:
                #0  0x00007ff57ca558f8 n/a (/tmp/.mount_krita-zVUO7G/usr/lib/libQt5Widgets.so.5 + 0x1628f8)

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/tmp/.mount_krita-zVUO7G/usr/bin/krita: No such file or directory.
[New LWP 1188734]
[New LWP 1188760]
[New LWP 1188802]
[New LWP 1188936]
[New LWP 1188833]
[New LWP 1188763]
[New LWP 1188761]
[New LWP 1188762]
[New LWP 1188939]
[New LWP 1200298]
[New LWP 1200166]
[New LWP 1188950]
[New LWP 1188801]
[New LWP 1188759]
Core was generated by `.local/bin/krita-5.0.0-x86_64.appimage'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007ff57ca558f8 in ?? ()
[Current thread is 1 (LWP 1188734)]
(gdb) bt
#0  0x00007ff57ca558f8 in ?? ()
#1  0x000000000ad3ba80 in ?? ()
#2  0x0000000000000000 in ?? ()