It’s definitely fixed on my UC5 current software 27.46. I’m not sure if it was fixed on this one, or one of the last two updates (didn’t run them long enough and didn’t pay attention).
My display/EVIC brightness is always set to the highest brightness before the “parade mode” detent. When I put it in reverse with the headlights on, the screen brightness doesn’t change on the reverse camera screen vs the CarPlay screen. Before, when going in reverse, the brightness of the reverse camera screen would go into full “parade mode” brightness.