In the past I had the same problem but there was an easy solution. Just turn off at the Evaluation -> Debugger in the main menu. But this time it is completely ignored. First of all I do not know why it came on in the first place but I tried flipping it off. When that didn't work I flipped it back on then off and that didn't work either. Not sure what to do next.
I also need to add that I had 4 tagged cells and just now noticed that my tags disappeared too. No other information was lost.
Edit: based on link in comment by Julian Moore it appears that this may be a bug in the Debugger. Unless someone informs of an alternate fix I intend to report this to Wolfram as a possible bug. I'll wait one week from today (5/5/21) or if or when Stack Exchange closes this question. Whichever comes first.