ToeKneeAy
I thought a little bit more about the power supply and wanted to also clarify another point: when the computer shuts down trying to power it on immediately does nothing. It takes around 5 minutes for the power button to become responsive again and turn the computer back on.

This led me away from the PSU being the culprit and thinking it was more a thermal issue as if it were just the PSU load, I would assume it would reset the computer but allow it to turn on again immediately once the load it couldn't handle was resolved.

Let me know if this thinking is flawed in any way. Unfortunately, if it's the PSU I won't be able to get my hands on one to test for a little while.

I'm having the exact same issue where the PC shuts down and can't be turned on for a while since getting an EVGA FTW3 Ultra 3080. X1 shows the temp is under 80 degrees but when I touch the coil on the GPU after shut down it's very very hot. What did you end up doing?
 
Update: I bought a new PSU and things seem to be stable now. I was using a Corsair CX750M, which only has 2 of the 8 pin PCIe connectors, but each cable splits into 2 for a total of 4. I recall some people questioning whether you need 3 separate PCIe connections from PSU to GPU on the FTW3 Ultra. I upgraded to a Corsair RM850X and left all the old PCIe and Sata cables plugged in to the devices as before (less cable switching.) Be very cautious about cable swapping from one PSU to another PSU and verify compatibility with 100% certainty online if anyone else is thinking about doing that. The new PSU is only 100 Watts more. I'm suspecting it may have more to do with the 3 separate PCIe connectors than the wattage in this case because I've read posts speculating this card has very high power spikes. Logically, if those power spikes get distributed to 3 separate inputs on the PSU (instead of just 2), I imagine there would be far less chance of a shutdown. 
 
Hope everyone else finds a good solution as well :)

Drumjod

ToeKneeAy
I thought a little bit more about the power supply and wanted to also clarify another point: when the computer shuts down trying to power it on immediately does nothing. It takes around 5 minutes for the power button to become responsive again and turn the computer back on.

This led me away from the PSU being the culprit and thinking it was more a thermal issue as if it were just the PSU load, I would assume it would reset the computer but allow it to turn on again immediately once the load it couldn't handle was resolved.

Let me know if this thinking is flawed in any way. Unfortunately, if it's the PSU I won't be able to get my hands on one to test for a little while.

I'm having the exact same issue where the PC shuts down and can't be turned on for a while since getting an EVGA FTW3 Ultra 3080. X1 shows the temp is under 80 degrees but when I touch the coil on the GPU after shut down it's very very hot. What did you end up doing?

Mine ended up being likely due to overheating of the PSU because I'm an idiot as ty_ger pointed out. I tried a new PSU and had no issues since then because I installed it the correct way. I would make sure you didn't make the same mistake as I did and that the PSU is getting good airflow or try a different PSU if you have one available or would be able to get one.

I have similar issue with yours, symptomps looks the same:
1. shuts down in the middle of gaming (temp max 74, not sure on the mem temp), but it runs ok in low load (non gaming),
2. Can only be turned on after couple minutes,

At first i thought my psu is giving up on me since im using evga ftw3 ultra 3080 + ryzen 5 5600x, paired with Antec Neo Eco gold 700 watt.

turns out my 320mm aio front mounting completely blocked with dust which blocked the airflow). Cleaned up everything and voila it runs smoothly again (tested with 1 hour gaming).

Really can’t ignore good airflow to run this beast.