Apple - How can I adjust brightness of 3rd Party external monitor on iMac, Macbook or Mac Pro via keyboard?
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.
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.
BRIGHTNESS MENULET APP (Free OpenSource code on GitHub, but you have to build it)
The app wil save you a lot of hassle over having to adjust brightness manually, but unfortunately isn't polished enough to be a product, so you need to build it, which unfortunately requires some familiarity with XCode and building macOS apps.
In macOS High Sierra, the app exited frequently enough (bug) that you'd have to restart it each time you wanted to adjust brightness. The workaround was to hit ctrl+spacebar to bring up Spotlight, type Brightness and relaunch Brightness Menulet App. Pretty quick. Not a big deal.
Fortunately, in Mojave and Catalina, the app doesn't seem to exit, at least not much, but the 'Follow main screen brightness' option no longer works, so I have to use the respective sliders in the drop down panel to control each Dell monitor's brightness. Works well enough because it just takes a few seconds and one doesn't do it that frequently.
How to build it:
- Install XCode and all its developer tools/command line tools.
- Install Brightness Menulet APP
- Build the Brightness Menulet app in XCode
- Install it into Applications.
You can use a pref make it launch at start (or use System Preferences, Users & Groups -> Login Items.
It creates an icon in the menubar that looks like a tiny Sun. Click it and the rest is self-descriptive.
Note: To bad this isn't available to typical users. It's really a feature Apple should provide since they pulled out the rug from people on 3rd external monitor support.
I think the reason it never became an app is that it's pretty tricky to make it work for all the monitors that it should support, and on all the macs and macBooks out there. Testing on all the possible configurations must be a nightmare.