I have 12 pro MAX with the same issue there is very little gap at top right corner and i have checked around 5 different 12 pro MAX , china version , USA and European one all has light gaps. technically it is not possible to have edge to edge fitting with stainless steel and glass and no matter how perfectly there is fitting there will still be minor may be 0.001 nm gap as per design. water can slip through no matter how perfectly screen is aligned with RIM edges. now coming to the IP68 rating. down the screen there is seal which will not allow water to slip inside the phone and that seal is there for water resistance
I really don't see it as issue or problem it is perfectly normal and at this type of design it can happen where screen is fitted inside the rim not on top of it.
feel free to use your phone the way you want. it is still safe to use and secondly IP68 doesn't mean to use phone at swimming pool water or any other like sea. once salt or cholerine will touch the seal it will chemically react with the seal and will make it damage
see the following screen replacement video to see how seal works.
hope answer the concern.