Comment # 8 on bug 1217750 from Takashi Iwai

Not really.  We still need to check whether nvidia-wmi-backlight stuff works or
not.

Meanwhile, when I reread the report, I noticed that the primary GPU is AMDGPU,
and this should have its own backlight control.  The hwinfo shows

  P:
/devices/pci0000:00/0000:00:08.1/0000:05:00.0/drm/card2/card2-eDP-2/amdgpu_bl2
  M: amdgpu_bl2
  R: 2
  U: backlight
  E:
DEVPATH=/devices/pci0000:00/0000:00:08.1/0000:05:00.0/drm/card2/card2-eDP-2/amdgpu_bl2
  E: SUBSYSTEM=backlight
  E: USEC_INITIALIZED=22270920
  E: NVME_HOST_IFACE=none
  E: ID_PATH=pci-0000:05:00.0
  E: ID_PATH_TAG=pci-0000_05_00_0
  E: ID_FOR_SEAT=backlight-pci-0000_05_00_0
  E: SYSTEMD_WANTS=systemd-backlight@backlight:amdgpu_bl2.service
  E: TAGS=:seat:systemd:
  E: CURRENT_TAGS=:seat:systemd:

Do you see the corresponding entry in /sys/class/backlight/*?

About which GPU: basically the primary GPU (AMDGPU) should be used unless you
specify with PRIME.  Some machines have a fixed connection of HDMI/DP to D-GPU
(Nvidia), but I don't know about yours.