Thanks. You confirmed my suspicion that the brightness of the displays cannot be adjusted during daylight operation of the car.
And I already do what you did: set the display preference for "night only". At least that gives me a more subdued light at night. But as soon as you connect Apple Play and display, say, a map during the day, its glaring brightness is distracting.
I find it odd that the Chevy engineers never even plugged in say, a bright app like the Apple road map, to come to the realization that the display should be dimmable in daylight, too.