iPhone 15 Pro Max Screen Makes Tapping Sound and Feels Like There is a Gap Underneath

Hi everyone, thanks in advance for your help. 😌

It has been 30 days since I bought an iPhone 15 Pro Max. I have no other issues with the phone but the screen is driving me crazy. It feels like there is a gap at the back of the screen. When I tap the keyboard to type, it kind of bends down, but not visibly. It is just a feeling in my fingertips. There is no visible gap, or at least I couldn't find one. However, the sound that comes out is definitely different from the other parts of the screen when I tap on the lower-middle part of the screen. It's like tapping on an empty wall instead of a solid one. It is the same whether there is a case or not. I noticed this when I took it out of the box, but I couldn't be sure. Is it normal that I get a different and noticeable sensation when I touch different parts of the screen? It makes me feel uncomfortable but I am not sure if it is a problem or just a gap.