At this point, I suspect something SUSE specific being the root cause here: While downgrading the firmware package did help and upgrading to kernel-firmware-20201005-337.1.noarch.rpm from https://build.opensuse.org/package/show/home:tiwai:branches:Kernel:HEAD/kernel-firmware did also work, just using the plain upstream amdgpu folder from https://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git and dumping it into /lib/firmware/updates works as well. (I used firmware_class.dyndbg=+p to check that the update files I fetched directly via Git are loaded).