Comment 20 for bug 1720438

I confirm that 'xbacklight -set 60' works (as user, no root required), in both desktop sessions: ubuntu and plasma. However, the Fn key + arrow only works on plasma.

Being on ubuntu session, inside the directory '/sys/class/backlight' there is nothing, yet xbacklight works. So it's almost sure a gnome/wayland whatever issue.

The graphics card is a nvidia 1060 on a gaming notebook, which you can switch to IGPU instead of DGPU on the BIOS but you need to reboot, doesn't have "optimus" or "on-the-fly" switching.

I'll answer here as well:

https://bugzilla.gnome.org/show_bug.cgi?id=688052