Well f me my new 4090 I got just did the black-screen 100% fan thing my previous one was doing.
I ran a 2060 for more than a week and played Diablo IV quite a bit and it never happened once.
Then I got the refurb 4090 and it's been perfect since.. Diablo IV, played through the entire campaign of CoD Black Ops 6, then a bunch of Sniper Elite 5... then just tonight it happened again!
The computer still seems to be going (as in I can still hear sound) for a while after the screen goes black.. once it did it while in YouTube and I could still hit the space bar and pause and unpause the video for a while.
I guess at this point it could be anything
Though one time it happened when I touched the CableMod power cable that I got while the computer was on (I thought maybe it wasn't seated fully), maybe that cable has a slightly poor connector or something, I guess that's the easiest/cheapest thing to switch out and try.