Twinkle Tray lets you easily manage the brightness levels of multiple monitors. Even though Windows 10 & 11 are capable of adjusting the backlight on most monitors, it typically doesn't support external monitors. Windows also lacks any ability to manage the brightness of multiple monitors. This app inserts a new icon into your system tray, where you can click to have instant access to the brightness levels of all compatible monitors.
Twinkle Tray uses DDC/CI and WMI to communicate with your monitors. Make sure you have the appropriate option(s) enabled on your monitor so that it can work with Twinkle Tray.