I am not sure when it started, but probably when I moved my NixOS config to flakes, I started noticing brightness changes on my login screen. It seems like it uses the built in ambient sensor, and I was able to disable it in my user settings just fine, but it drives me crazy on the login screen, especially since I have to change the brightness when I log into my account!
It would be amazing if I could somehow change the dconf option [org/gnome/settings-daemon/plugins/power]
to ambient-enabled=false
for the gdm user, but I am not sure how…