I bought a 2021 Yukon XL Denali and after a few days had this same issue. I had paired my cell phone so thought it was causing this to happen. Unpaired and disabled Android play. Thought I fixed it but then got it again while picking up groceries at Walmart which made it difficult to back out. Went home and thought a bit about what was different from the previous times I started the vehicle. Like your laptop or home computer you have to wait for it to boot up and complete the startup sequence. I now wait for the GMC image to complete and hear the running boards close before I push the start button. Haven't had a single camera failure since doing this. Might try to see if this works for you.
