Search in Mail stopped working in Big Sur

I confess that I haven't tried Safe mode yet, but I don't see it as very helpful because I can go a week without any problems and then all of a sudden searching no longer works in Mail. And it isn't practical to work in Safe mode for that long. Let me try giving a little more info to see if anyone else is having this issue. When searching in Mail stops working, it still gives some response. For instance, if I type one letter, I may get one name from my contact list. As soon as I type any letter other than the 2nd letter from that name, I get zero results. And with some letters, I don't even get a name even though I have many contacts that begin with that letter. For instance, if I type "a", I get some mailboxes which have an a in the name but nothing else. I went through the entire alphabet, one at a time, and got a total of 4 names from my contact list. And I never get the usual "Subject contains...." Every two letter combination I have tried produces zero results and a few single letters, like "v" does the same even though there are mailboxes that have a v in the name. So there is no rhyme or reason for why some letters give me some results but not other letters.

I don't have to restart to fix this, logging out of my user and back in will do it. Just a pain to do every time this happens.

Well the fix only works partially. I still have several months that do not appear in the search results, forcing me to search manually through thousands of emails for the email I need. I sent feedback to Apple.

Can't wait to try this the next time search fails. I will post a report when that happens. I will also report it to Apple. Many thanks!

This indeed did the trick! Opened up Activity Monitor, found 'corespotlightd' and quit it. Bingo, search in Mail works again! Many thanks!