I agree. There are brightness sliders for each screen in System Preferences, but doing it that way is a pain in the butt for something that I do frequently. My

I agree. There are brightness sliders for each screen in System Preferences, but doing it that way is a pain in the butt for something that I do frequently. My previous laptop was a 2012 Macbook Air, and I used an Apple Bluetooth keyboard at my desk in part for this reason. The laptop keyboard adjusted the laptop screen brightness, and the BT keyboard adjusted the external screen brightness.