iMac 2015: no options to adjust brightness, /sys/class/backlight folder is empty

[x-achilles-o]

Dear fellows,

my iMac 16,2 from 2015 with Intel Iris Pro Graphics 6200 has no options to adjust brightness. It is constantly on max, which is really not pleasant to the eyes. Many solutions found on the net involve the /sys/class/backlight folder but in my case this ones empty. I already tried from this wiki the kernel options - no change - and the XServer config - creating the 20-intel.conf file also brought no changes.
Is this even solvable? I would love to understand why its not working on my iMac.

[x-achilles-o]

Output of

lspci -k | grep -EA3 'VGA|3D|Display'

says

00:02.0 VGA compatible controller: Intel Corporation Iris Pro Graphics 6200 (rev 0a)	DeviceName: Integrated Video Controller	Subsystem: Apple Inc. Iris Pro Graphics 6200	Kernel driver in use: i915