Windows 10
AMD 2700X CPU
x470 AORUS Ultra Gaming mobo
32GB of ram, half 3000 MHz, half 3200 Mhz
2 Corsair MP600 nvme drives
1440p 144hz main monitor
1080p 60hz second monitor

and then the current focus of my issue, a Gigabyte 3060 OC 12GB

I have been seeing this sort of artifact on my monitor:
https://imgur.com/a/6J9plWA
it happens the most with youtube, and less commonly with other websites. that's more a matter of how much time I spend on youtube. it will appear for a second or so and then disappear, and then won't happen again for about 10 or 20 minutes.

I have tried:
-fresh installs of my nvidia drivers, DirectX 12, windows OS,
-swapped HDMI cables and monitors,
-played with the monitor's refresh rate and resolution,
-incidentally upgraded my drives from SATA to M.2 and added 16gb of ram in the time that the issue has been around, since I don't think the issue is connected to that anyway

The artifact still appears over the browser window, on either screen and where ever the browser window is on that screen. full screen games may have some issue with frame skipping, but it's hard to tell if it's in my head or not. sometimes it feels like I'm getting gaslit by my PC. I have had it RMA'd and Gigabyte made some sort of repair attempt and sent it back. The issue is still happening, and was actually worse yesterday, staying on screen for a whole 10 seconds.

Does anyone know what this could be caused by?
Is there anything more I can try to diagnose or fix the issue?
Is there somewhere else I should ask for advice?
Is there another component in my system that could be causing this behaviour?

P.S. Just found this other reddit post on what looks to be the same issue:
https://www.reddit.com/r/pcmasterrace/comments/zoxwm1/black_squares_on_screen_flashing_for_half_or/
no definite cause or fix mentioned tho :(