Most desktop monitors have their brightness & other config exposed via the DDC (DDC?) protocol. This is a simple UI that exposes the brightness controls on Windows. Much easier than using the buttons.
You might need to go to the monitor's menu and enable DDC if it's disabled by default.
On Linux this script works for me:
sudo modprobe i2c-dev; sudo ddcutil setvcp 10 $1 &
Thanks! I've been looking for this!
On macOS I've been using https://github.com/the0neyouseek/MonitorControl -- which also lets you use the brightness keys to control external monitors.
My monitor has terrible "buttons". This utility means I no longer have to fumble around with them to adjust the brightens. Thanks for the link!
I can't believe I'm only just now finding out about this. Do you have any idea why this isn't something built into Windows?
Windows has a brightness slider in the side bar, but it doesn't seem to work with external monitors. Probably because OS-level brightness controls were implemented when laptops became popular, and traditional PCs with external monitors became an afterthought.