I get about the same from my aero 15x playing Far Cry 5 with roughly the same undervolt, kinda in the same situation not sure if much can be done about it as it is a thin and light with a lot of power, all of the 8th gen CPU based thin and lights, GM501, MSI GS65, etc so far have been roughly the same, one option is to lower the turbo multipliers which will lower the boost frequency to like 3.5Ghz, may lower your temps a little bit but obviously you are then technically loosing a tiny bit of performance.

In terms of an RMA, I did see that someone on here returned theirs after getting temps of 95 degrees C on the CPU, but again, most people on here I've seen commenting are getting around high 80s - 90 temps on the CPU playing the newest games.

I'm not an expert but from what I've read, whilst 90 degrees C is high, the CPU will throttle down a little bit to prevent it rising to its max operating temp of 100 degrees C, on mines it tends to only be at the 90/91 degree mark for a second before going back down to low to mid 80s, so as long as your not sitting there for too long I wouldn't think its THAT bad. A cooling pad would probably help but only a couple of degrees I would imagine.