So I actually created a similar issue with mine today. I did a full shutdown and booted back into the BIOS. Did a case reset, loaded up the default values (no DRAM profiles) and rebooted. Then directly back into the bios. Loaded my old profiles but made one change which was disabling the Serial Com port. Rebooted into Windows 11 normal but then suddenly got the rectangle artifacts. Then the PC just rebooted on its own, no BSOD. I updated the NVidia driver on my RTX 3060 and rebooted. The problem hasn't returned. I've never seen this before but it only occurred after I went into the BIOS and did the things I mentioned previously. Also never had this PC just reboot on its own with no Windows warning or BSOD. Somewhere there was a hardware/Windows conflict when it rebooted into Windows the first time. And BTW, I left that serial port disabled so that wasn't it. I also don't think it was a graphics driver problem.
I think these motherboard BIOS's become unstable from time to time. I did a full case reset and BIOS default/reboot thing because it always fixes a problem with the on-board Realtek NIC occasionally not loading up after the system comes out of sleep/hibernation. A full shut down with the power supply button off along with a BIOS case reset is the only thing that fixes that issue. This time, I did a couple additional things and created this stability problem at the motherboard level, which affected Windows in two ways. One with the rectangles and two, with the sudden reboot. If I see this again, I'm going to swap out the DRAM modules and see if maybe that's the source of my instability. Maybe the DRAM stick's EMP's are being affected over time and especially when the PC comes out of sleep mode.