Monitor that I can control its brightness from keyboards/OS settings section I am stuck with a 2008 Apple Cinema Display because every monitor I try, I can not control its brightness from the keyboard and that's a must for me.

I am unsure what I should be searching for to get such monitor. I change the brightness multiple times per hour so I can't simply reach to the screen to make the adjustments. I absolutely need to control it via keyboard.

What are some of the available monitors that allows such functionality and why it's possible with them and not the others?
Check if your external monitor supports DDC/CI. If so, you can use this app to adjust the brightness using your keyboard.