Apple LED Cinema Display Brightness controls not working on a M1 Mac mini with Monterey.

I had this same issue with my M1 MacBook Air and a 27" LED Cinema Display. It seems the display is no longer supported under Monterey and ability to control display brightness and automatic brightness adjustment have gone away. I found a discussion on Reddit (linked below) describing the same issue, which ultimately led to installing an app called MonitorControl. Once installed I had to set the DDC max for brightness to 255 and it now behaves as before. The controls will not work in control center or system preferences, but brightness can be adjusted through MonitorControl or shortcut keys. I have not been able to figure out how to disable the automatic brightness adjustment (never liked that feature), but for now I just covered the sensor with some black electrical tape and it no longer attempts to change the brightness on me.

Reddit: https://www.reddit.com/r/MacOS/comments/qk64ab/led_cinema_display_brightness_option_greyed_out/

MonitorControl: https://github.com/MonitorControl/MonitorControl

The LED display should have 2 connections, the Mini-DisplayPort and a USB-A plug. Are both of them connected to the Mac mini? You will need 2 seperate adapters for both connections to 2 USB-C ports.

Is the display's USB-A cable plugged into the Mac mini?

Fingers crossed... I've been hoping for something to fill the gap for several years now. I never thought I'd still be using this display almost 12 years after I bought it in 2010 😆. It's a great display, but it's definitely long in the tooth.