I have had the both the same brake squeal and dimming issues in both my 2021 XT5 and XT6. I suspect the light sensor is in the front of the car. Try backing in and see if that solves it. New brake pads are on back order, Ugh! . My service writer admitted there is a problem with the composition of the pads. I can't believe that they didn't pick that up at the factory. I guess that figured you wouldn't hear it with the radio on. No fix for the dimming yet. In my experience updates have never been a focus for GM. "Working as designed..." It getting hard to be a devoted American Car Buyer.