Today BMD has released ATEM Switchers 8.5.1 update which improves input and monitor compatibility for all ATEM Mini models, as well as the ability to adjust button brightness to suit working in all lighting conditions.
This update also lets you retain up to 20 still images in your media pool between power cycles on ATEM Mini Pro and ATEM Mini Pro ISO, so your images will be saved when you turn your power off, ready to use instantly on your next production.
In ATEM SETUP you can find the Button brightness slider.
Button brightness at 100%
Button brightness at 1%