I went from an EVGA GTX1070 SC to a 3080 FE and the power draw requirements are significantly higher. I also replaced my PSU (went for a Corsair RM750) to avoid any potential PSU performance issues due to its age. I've had issues in the past with PSUs becoming less able to deal with transient power spikes and very high current draw as they've aged, caps have dried out, etc.
If you reboot in Safe Mode, does the GPU reliably work for more than several hours? Obviously you can't test 3D acceleration, but you can at least run Furmark and do some CPU benchmarking to keep thermals up at gaming level temperatures.
If the GPU output still displays after 3/4 hours when it would have cut off in normal mode, it's one indication that its 3D acceleration features may not be working well. Could be hardware, but could just as well be driver problems.
From Safe Mode, try a
full DDU driver removal then a fresh install of the latest drivers. Doing this cured some black screen issues I had a couple of years ago with a GTX 1070.
If that makes no difference, I would boot back into normal mode, then keep a close eye on the card's power draw and temperatures using the latest version of HWiNFO64 running while you use the PC. Be sure to enable logging first in HWiNFO, then you can review the logs with the developer's accompanying log viewer app (called "Generic Log Viewer" if you do crash and have to reboot. You may find that the PSU is shutting down power supply to the GPU if it's attempting to demand more current than it is capable of delivering in a short period of time (a transient spike).
You could also try installing MSI Afterburner and reducing the Power Limit to 80% or 90% to further see if it's related to unachievable power demands by the GPU on the PSU.
Other apps like OCCT and RealBench can apply simulated benchmark and stress test loads to the GPU as well as the CPU, so you can stress test your machine at similar levels to demanding gaming or desktop editing/rendering.
Do you also have integrated graphics which you could enable in Windows, so you could plug your monitor to that if the 3080 shuts down again? You could check if the entire PC is frozen or if it's just the card shutting down suddenly.
If after all that fault-finding comes up with nothing, I'd be tempted to RMA the GPU. It'll be a hassle if you leave it until the warranty period is up. Good luck...