It’s a known issue with most of phones. This had happened in my phone as well and fortunately for me, my phone was within the warranty period and so the screen was replaced for free at Apple service center.
Apple is aware of this issue, contact Apple customer support and fight you case and they might still help in getting your display free of cost, but again you have to fight your case to get the free replacement.
This has been reported by many users and a simple google search for iPhone 13 Pro Max display issue will prove this point that it’s known issue.