Slow search on Mac OS Big Sur

Like lots of others mail search stopped working correctly in Big Sur (in my case not the initial installation but after one of the many upgrade). Following all the suggestions I tried just about everything. I rebuilt all the spotlight indices and even did a clean install of the OS. After all that, searching would work briefly but then either not work or delay for several minutes until it actually searched. After a couple of successful searches, the mail search would be unable to find anything. Sometimes restarting Mail would get it to work a few more times. Sometimes logging out and then back in would restore limited function, but the only sure fire solution was to restart the computer after which the Mail search would work perfectly for a while & then go back to its old tricks. One of these posts suggested EntreCheck Pro which I had never heard of. Being desperate, I installed EntreCheck & ran it. Nothing super serious was found but it reported that a daemon from Retrospect was consuming an unusual amount of system resources. I had not used Retrospect in several years so it was way out of date. Being a bit unsure of how to rip out all the pieces of that software, I upgraded to the newest version and let their software do the dirty work. Immediately, mail searches started (and continue to) work as expected. The daemon causing the problem is supposed to flag changed or new files for backup by Retrospect. My guess is that the out of date daemon kept flagging and indexing the mail spotlight files causing endless loops. So in keeping with the season, I guess we need to watch out for zombie software daemons. CK