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?