https://bugzilla.kernel.org/show_bug.cgi?id=196117
--- Comment #2 from Michel Dänzer (michel@daenzer.net) --- Sounds like maybe some files under /lib/firmware/amdgpu/ are missing in the initrd. In order to get more information, try booting with
modprobe.blacklist=amdgpu
on the kernel command line and then run
sudo modprobe amdgpu
manually and check dmesg.