Hi!
I recently got the 13 Pro Max, and after standing in direct sunlight noticed a gap at the top of my phone. It’s not even 0.5mm, but was enough for me to be concerned. I have been to 3 phone stores and checked display models, and out of the 6 iPhone 13 Pros and Pro Max’s I saw, all 6 had a gap at the top, or on one side, or at the bottom. After speaking to Apple support, they told me this is a discrepancy within Apples tolerances. Replacements may have the same issue, or have it worse. It’s a lottery. It won’t affect water resistance, nor will it affect dust resistance. All technology will have imperfections, it’s a fact of mass production. Not to mention glass and metal shrink and expand in different temperatures, so if the screen were flush on all sides with the frame, it would cause damage and warping over time. Obviously the aim is to have the screen centred so the gap is equal on all sides but again, with mass production that simply isn’t possible.
Bottom line, it’s an expected discrepancy. Apple consider it cosmetic, and are unlikely to do anything about it. Even if they do, and they exchange your device, you could end up with a worse gap. Perfectionism is a problem, Apple I think need to drop their perfectionism because their technology is not without flaw and by pedalling it as this flawless item, people notice the imperfections so much more