How can I adjust brightness of 3rd Party external monitor on iMac, Macbook or Mac Pro via keyboard?

I have been using Monitor Controll - https://github.com/the0neyouseek/MonitorControl - for a couple of months now with a Dell screen, and I have only words of praise.

I've found Lunar.app and it syncs the brightness from your PC to the external monitors. It has a lot of other features that I not yet have played with, but a uniform brightness is already great. The app looks nice, so thats a plus (and it's free).

Here is an article on lifehacker.com, because the information on the Lunar site is really sparse.

Using Luna would help in this case.

It will basically sync your primary screen brightness, as well as the other necessaries to your second screen.

Check this out: https://lunar.fyi