I’m running NixOS with GNOME and it doesn’t seem to recognize the keyboard backlight(s). GNOME has a quick settings tile for this and it doesn’t show up.
Is the backlight controllable from software at all?
Is it possible to make NixOS/GNOME recognize the keyboard backlight without customizing the firmware?
Are you using the white backlight (standard keyboard) or the rgb keyboard?
You could try using Framework’s provided keyboard customization website here
You can also check out the Framework 16 support page and if you scroll towards the bottom, there are links to using the keyboard and see if you can solve the problem.