On my 2019 LT, the dimmer button does nothing to the screen when the backup camera is on. When I put it in drive, the "regular" screen (radio, climate, etc) respects my dimmer settings, but whenever the backup camera is up and I'm in reverse, it's full on stadium lighting.
Pretty annoying, my wifes 2016 Malibu adjusts with the dimmer, and that's an LT also.