I myself dealt with random black screens. screen would just go black for a few seconds and come back. I never experienced reboots, crashes, locks ups, etc.
But after the new build and 2 weeks of trouble shooting it came down to 2 things.
 
1: If you are using a 4k tv "not a monitor" a tv. make sure in the tv settings you have the hmdi port you are using is set for the correct signal. For example, I have a Sony x85K 4k tv 43" after sometime I found out  the hdmi port I was using needed to have the setting on that port set to "VRR" which makes it compatible for pc's. This fixed my first issue of garbled screens when joining games.
 
2: The ultimate fix was me trying every high quality hdmi cable I could find. Bought 4 of them one was $50. None of them made the black screen go away. Finally after some advice from Hemi on here in the forums, I bought the cable he had. Specs were all the same I been buying. But his was a 6foot hdmi cable. All my issues have now been resolved. Doesn't matter what hdmi cable you get as long as its made for 8k and 4k just don't go over 6ft! Yea, I know... its doesn't fit with your set up and it didn't for mine either but I made it work and moved some things around in the office.
 
Do these two things and see what you get. Forget all the other try this setting and that quick fix. None of them worked for me and i would be surprised if they did for you.
Good Luck!

I'll add myself to this list...
I also have the 'screen goes black for up to 5 seconds, then comes back.
This never happened until like a month ago.
I have Windows 11 (full version, not 'insider' beta):
Intel NUC12DCMi9 - the toaster sized Intel PC with i9,
32GB ram, 1 TB SSD, and EVGA RTX 3070 Ti
 
It happens regardless of use - like twice while reading through this forum post...
When it happens while gaming - it is a nightmare, sometimes causing failure of fight - not good for such an expensive gaming system. This is my Media pc - connected to my 4K TV via HDMI on feedthrough of my Yamaha RX-A8A 7.1.4 Dolby Atmos surround system.
It ran from last July through January with 0 black screens... now at random, minutes to hours between, load independent, with latest Nvidia drivers.
My guess is a recent driver change - since it is new on my PC.

Update: A week after posting this and messaging/talking with EVGA support, their only guess was lack of power, so I decided to make sure it wasn't the lack of power in my Intel NUC12DCMi9 with it's integrated 650W power supply - so I purchased a Thermaltake Smart 430W power supply, and a cute little ADD2PSU board that receives the NUC12DCMi9 Molex 4-pin power cable that acts as a switch to instantly turn on the 430Watt power supply when PC power comes on for $54. Now the EVGA RTX is powered from its' own power supply.  No difference - proving it was not lack of power.

Solution:
Next attempt as lascivious1 had suggested above, I purchased a new HDMI cable:
I bought a "Highwings High Speed 8K 60Hz HDMI Cable 3.3FT/1M, 2.1 48Gbps HDMI Braided Cable"  from Amazon - the important considerations were 20,000+ 4.7 star reviews and 8K 60Hz/4K 120Hz support as there are many cheap 8K cables listed that are older 4k/1.1? cables relabeled for profit.
This worked - I have had zero black screens since upgrading to this cable!