Driver problem
I used ASUS TUF-RTX3080-O10G and encountered the same color patch under the desktop several times.
The magic is that after refreshing the desktop or rebooting, the color blocks will disappear.
Later, I changed it to EVGA 3090 FTW3-ULTRA and encountered it once.
So I don't think it is a problem with the graphics card hardware.

I got a couple of Startech 1.4 cables and it did seem to work. However, I started having other issues with the monitor. I ended up buying the XG27UQR and it just works. The XB273K never worked correctly.

Alright, so this is kind of crazy. It came back today. I booted and this was happening again. I've changed out the cables, got a new monitor and also got a new graphics card... What else could it be, a Windows bug?

Sajin
3090 firmware issue that affects certain monitors? Driver issue? 

I wonder if somehow the HTC Vive that I leave plugged into the graphics card, but never use, is the issue somehow? I also wonder if it has to do with turning off CSM in the bios to enable resizable bar? Maybe, the PCIe slot? It’s really difficult to pin down because it rarely happens. It also only happens randomly when first booting into Windows from a cold boot. It never happens when restarting or randomly after the computer has been running for a while. If it doesn’t happen at boot, it won’t happen at all.

I might also try a clean Windows install. The last time I clean installed was when the 8086K first came out about 4 years ago.