(In reply to Takashi Iwai from comment #9) > Ah, that's what I wrongly remembered, sorry. > > But yes, testing with nouveau once would be interesting. This also allows > testing with other older kernels more easily, too. Switching to nouveau made no difference. The last kernel allowing me to change display backlight is 5.7. So I guess the issue is introduced in kernel 5.8. I'm attaching the dmesg and hwinfo next.