thanks for good infos 
At first the question: if you had former in game the DX12 setting choosen, then you should revert that
Otherwise I have currently only the usually cleanups in mind ( AppData : DCE, Scenery * , content.xml , rolling.cache ) , may be additional the Shaders ( windows cleanup , and may be additional the nvidia caches AppData\Local\NVIDIA\ * Cache)
And yes, allways try without any other tools running ( e.g. Afterburner ).
If all will not help, try to set a fps limit in nvidia control center ( a low value, e.g. 30 ).
And to be sure: you get that popup about " graphics device has encountered a problem " , or not ? Because then the other topic is better because other reasons are possible too then ( from xmp mode , or the need to disable HAGS, but not for all users it worked ).
PS: a note, 850W and a 3090 can be a bit edge case