Mystery logoff

[MR ZenWiz]

I have been running  an AMD 9 59590X CPU with 32Gb of RAM andan ASUS
mobo since late November.  I found out after upgrading my primary
desktop to this that I could not run video without an external card,
so I added a Gigabyte GE Forsce 1030 (after two other cards failing to
run right) and Xubuntu 21.10 (because older releases could not handle
the CPU at all). I am using the Nouveau video driver bcause I've had
issues with othrs, especially the Nvidia native ones, and I don't care
to deal with that.

Things have been going fairly well except for an occasional mystery
system stop (black screen, no k/b or mouse response) or surprise
logoff, usually when I'm not working on the machine.

Today it happened again and I was able to find three logs that might
help: kern.log, Xorg.0.log.old  and apport.log. These occurred about
an hour before I tried to log in again, and there is some info in
there I'm hoping will help.

Problem is, I don't have a clue how to read the logs, although it
looks fairly clear that Xorg crashed, possibly because of an error in
nouveau.

I really need help deciphering what these logs show.  The files are at:

kern.log - https://drive.google.com/file/d/1kSRBHGP1RNKncp_zWyaGzMI3Ln3dXKZI/view?usp=sharing

Xorg.0.log.old -
https://drive.google.com/file/d/1XgXHeHpe1UpXwVLpa0FH2Cbf8K13dLjD/view?usp=sharing

apport.log - https://drive.google.com/file/d/1kSRBHGP1RNKncp_zWyaGzMI3Ln3dXKZI/view?usp=sharing

If anyone has a clue, please let me know.

Many thanks!

Mark