Comment # 91 on bug 1177428 from Takashi Iwai

It's hard to say.  We used to have a workaround (keeping the old firmware file)
for Vega10 in Leap 15.1 and Leap 15.2, but this was dropped in TW (hence also
Kernel:HEAD and Kernel:stable) as well as Leap 15.3.

So, if you have kernel-firmware-all package on your system (not
kernel-firmware), it means you having the latest firmware from TW/Kernel:HEAD,
and the workaround in the firmware was gone.  And, IIRC, this problem depends
on the hardware setup such as the backlight level, so the upstream couldn't
reproduce the issue.

If you see the problem with the latest TW kernel and with the latest
kernel-firmware-amdgpu package, you should report the problem to upstream and
resolve the bug there at first.