The top line on my iPhone XR isn’t showing

What do you mean it isn't showing? Is anything showing there, if you rotate the phone, does it work at that point in that area? If when you rotate the phone you still don't have anything in that area of the phone, there may be something wrong with the screen itself. If you see it there, perhaps a little more detail on what exactly you are seeing, we might be able to assist you with some other things to try.