In one Review of the RX6900XT the highest temperature recorded under stress or heavy loads was hot spot of 97C.
Okay I just had a Chat Session with AMD Customer Service when I went to the AMD RX6800XT Page that shows the specs. this is what he suggested concerning the RX6900XT:
I would just keep it under 90c for sure on the Current temps and under 110c for Junction temps
So it seems like the RX6000 Series GPU cards have the same Maximum Operating Temperature of 110C for the Junction or Hot Spot Temperature.
Derrick G. - AMD Customer Service also mentioned the best program/software to configure the RX6900XT was AMD Wattman and to avoid using any other 3rd party software like MSI Afterburner.
Since AMD Wattman is part of the AMD Driver package and engineered for AMD GPU Cards.
I mentioned that reviews seems to show that the Current or Normal Temps under heavy stress are around the Mid 70C to Mid 80s C. and the Hot Spot (Junction Temp) was around 97C. Derrick said that sounds about average for that card.
NOTE: Seems like AMD added a Customer Service CHAT LINE now which was a pleasant surprise to me. Since I am hard of hearing this is the best method of communicating with Support, at least in my case.