UPDATE: I went to the Apple store and I spoke with the Genius Bar. After testing the camera he told me that this is lens flare and it is just normal on every iPhone 11 pro and pro max especially when using the night mode.
Thus, he noticed a small scratch on the rear camera, which is a manufacturing defect, but it does not affect, in his opinion, the quality of the shots. He made some tests and he told me this is a cosmetic issue not a functional problem, and if you want to swap it you must ask your certified reseller (where I bought it) to replace it.
I bought this device only one week ago, do you think worth it do exchange a phone for a small little scratch on the camera, which do not affect (I think) the quality of the shots?
I wouldn’t exchange it and find myself with another issued device.