Long-time reader, first time poster. I registered just to offer what appears to be a solution for me.
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@Scallywops the symptom was a black screen and GPU fans screaming, but the soft-power-down button on the case would always lead to a gentle shutdown. Often, this was in Microsoft Flight Simulator 2020, which is very hard on both GPU and CPU, but rarely it would happen outside a game.
Scallywops' research on behalf of us all in swapping out parts and trying other things was very helpful, so at a similar loss (but without the swapping out of parts - no part really seemed to be failing) I looked for configuration issues, but didn't find anything promising (XMP off, no over-clocking of GPU or CPU, etc.). Further, while I had this problem last year, it eventually stopped happening, but resurfaced in the past few weeks. GPU and CPU are NOT overheating; GPU temps top at about 62 degrees C.
So...what could have changed in the past few weeks, except...
the weather?
Finally, I think I have found the problem and, for me, the solution:
THE POWER SUPPLY WAS OVERHEATING
My Seasonic Prime Gold 80+ 750w seemed to be working perfectly fine, and while I considered swapping it out (it's 3 years old), other people with this problem replaced theirs with no change in behavior.
Finally I paid attention Hybrid Mode on/off switch on the PSU, next to the power switch. Mine was currently set to Hybrid Mode ON, which I don't think was intentional - I probably accidentally pressed it while looking for the power switch. Getting out the Seasonic documentation, I found that the way that I had mounted it called for only the Normal mode to be used (in Hybrid mode the PSU fan should face the motherboard; my case has a bottom grill/outlet).
Changing the switch to Normal and...3 days later I get -0- crashes, despite numerous hours running MSFS, including some of the new resource-intensive jetliners.
I hope this helps someone.