DispCtrl

DispCtrl for Linux warms or dims any display through its gamma ramp, keeps
a night light schedule, arranges displays, sets a laptop panel's
backlight, and brings Windows 11's snap layouts and Snap Assist to X11
desktops. A small engine started at sign-in keeps it all applied; the
window and the dispctrl-linux command both talk to it.

It needs an X11 session: on Wayland the compositor keeps gamma and window
placement to itself.

Not in the snap: an external monitor's own brightness over DDC/CI. Strict
confinement cannot reach the I2C buses; the .deb and the tarball from the
project's releases can.

The laptop backlight needs one permission the Store does not connect by
itself yet:

sudo snap connect dispctrl-linux:login-session-control https://github.com/HaythmKenway/DispCtrl/blob/master/docs/LINUX.md