Extend right is an option from the screen menu opened with Win+P (or Fn+F10 on my laptop)
I have better diagnostic now : when I reboot my computer in that mode, it triggers the issues I presented above; when I go to sleep and resume, I have other errors.
I didn’t edit any of those files manually, the worst I did was run a command/program.
Both /etc/X11/mhwd.d/nvidia.conf and /etc/X11/xorg.conf.d/90-mhwd.conf are empty (they only have a “generated by mhwd” comment).
I don’t know where to look in .cache for problematic files