Similar thing happened to me recently. I purchased the iPhone 11 Pro in late December, less than a week later a single crack similar to yours originating from the corner of the camera block appeared. To my knowledge the phone never sustained any impacts (e.g. was never dropped, was never inadvertently bumped against an edge etc.) . I always keep the phone in a sleeve when not in my hand, and it's usually in my front pocket when not in use. The only environmental impact I can think of is that during the day I noticed the crack I was outdoors in below freezing temperatures for an extended period (~3 hours) and then went inside a warm house. So the phone would have gone through a ~25 degree Celsius change relatively quickly. I think it's a manufacturing defect, but not surprisingly Apple won't accept responsibility.