I have 2 external displays plus the built in one on my iMac Pro. I was happy to see that BTT can control the brightness of an external display, not just the main one — lots of tools cannot.
However, it seems I can only control the brightness of 1 built in display and 1 external display.
I created a keyboard action to do 3 actions: "Brightness Up", "Brightness Up (External Display)", and "Brightness Up (External Display)" again. However, the final 2 actions just increase brightness on the same external monitor, leaving the third screen unchanged.
Any way to control brightness of ALL displays?
the external one should adjust the brightness for all external displays that support software based brightness change.
Can you change the brightness for that display in System Preferences => Display?
Yes; these are identical LG UltraFine 5K displays.
I have read reports (pertaining to other tools) that sometimes monitors are supposed to report some kind of unique ID, but they report all zeroes (or similar) so the tool cannot differentiate the monitors.
Maybe something like that?
But yes, if I open System Preferences and go to Displays, I can use the slider to adjust the brightness of each display reliably (but annoyingly lol).
ah, the 5k Ultrafine is very annoying in that regard. I have added support for it to the Touch Bar brightness widget, maybe I can add that as a predefined action too.