If it was running great until Monday, did something change? Do you have auto-updates enabled? Yes, I did; I don't now.
If there was a SW update, I would suggest going back to an older OS version of Big Sur, or maybe back to Mojave or Catalina. If anything, just to test to see if your HW is working correctly, but if you have no reason to run newer OS versions, just stick with stuff you know works. It's a little late to do the right thing now. But I've learned a lesson. And I do not know how to uninstall an update. I was incorrect on the days I said earlier. It happened on Monday, May 10th not the 3rd. I checked and my update to Big Sur 11.3.1. occurred on May 6th.
I think you may have forgot to post the photos. They are posted now.
Can you post the adapter you purchased? It's posted below.
My guess is that it is SW related, or maybe something wrong with the HW (maybe GPU?) of your Mac, but I am betting on SW/OS related.
While I do think it is probably an update that broke the external display, it probably wouldn't be a bad idea to run an Apple Hardware Diagnostic Test to rule out anything HW:
Apple Diagnostics, formerly known as Apple Hardware Test, can check your Mac for hardware issues.
support.apple.com
Basically, hold down the "D" key on startup, and give it a few minutes to boot up. You can let go of the "D" key when you see the globe.
Note: In my experience, the Apple Hardware Diagnostic Test gives a lot of false negatives, meaning it might say all the HW is fine, but there is a problem. So, just because it passes doesn't 100% mean that your HW is good.
But, I don't think it ever gave me a false positive before, with the exception of it saying that there was a problem with a fan, but it ended up being dirty not failing. Thanks for all your feedback. I will try the hw tests and most likely buy a new HDMI cable to see if the other one is bad.