There is also Clight (https://github.com/FedeDP/Clight) if you want automatic backlight adjusting given ambient brightness. It supports external monitors through ddcutil C library and has many more features to offer.
Disclaimer: i am its creator ;)
I've tried setting up clight on various occasions and now gave it a shot again, whilst I appreciate all the documentation I'm still struggling to get it working on NixOS with swaywm on a laptop. I'm primarily interested in adjusting screen brightness based on my webcam. I'm already using redshift/gammastep.
Uh that's sad! There is actually an issue opened about NixOS; but, since I am not using it, it's pretty hard for me to debug.
If you want some help you can comment on that issue though!
