This application was originally light and simple, for one monitor.
https://www.tonymacx86.com/threads/nativedisplaybrightness-with-gui-fork.256152/
Control your desktop monitor brightness just like on a MacBook!
This a utility application to control the brightness and color temperature of an external monitor directly from your keyboard.
Use the F1 / F2 key to decrease / increase the brightness of the external monitor. If you have an Apple or similar keyboard, you probably need to also press the fn key.
Also you can set any key from F1 to F20 in the settings for changing of brightness or color temperature.
For a finer brightness level adjustment, you add the option key, i.e use Alt + F1 to decrease the brightness, or Alt + F2 to increase it. Also you can enable smooth step in the settings.
This app shows the native system UI when changing brightness! It uses the private BezelServices framework for this.
Your monitor needs to support DDC/CI for this app to work. If you don't see the brightness system UI displayed on your monitor when pressing the F1 / F2 keys, this means that your monitor is not supported.
If your monitor supports reading the current brightness value from DDC/CI, the app increments / decrements the brightness starting from the monitor current brightness value. This allows you to set the brightness using the monitor's OSD and to adjust it later with the app
If you have multiple external monitors connected to your Mac, the brightness adjustment is done on the monitor with the currently active window, and the brightness system UI is displayed on the adjusted monitor.
macOS version: 10.12.4 or later
This application uses code borrowed from ddcctl which uses code from DDC-CI-Tools
GNU GENERAL PUBLIC LICENSE