I'm running an RX 6800xt and ryzen 7 5700x with a corsair rm850x and have been experiencing random power offs and game crashes. I've tried DDU, reinstalling windows, and a different psu but no luck.
What are temperatures like when it shuts down? Check the motherboard BIOS to see if there is a max temp configured.
Temps are around 75-80°C There's no temp limit in the BIOS.