Hello.

If you're using an AMD GPU, you won't be able to shutdown or reboot correctly your computer.

This is a known issue on kernel bug tracker : https://bugzilla.kernel.org/show_bug.cgi?id=207331

And I reported it on Archlinux bug tracker too: https://bugs.archlinux.org/task/66305

I tested proposed patch, and it works. So let's hope for a fixed kernel either from kernel hackers or Archlinux maintainers.