Mail has always been spotty, but Mail's search completely stopped working for me around the time I upgraded to Big Sur. Currently, it finds only a few random s

Mail has always been spotty, but Mail's search completely stopped working for me around the time I upgraded to Big Sur. Currently, it finds only a few random scraps and doesn't search the entire mailbox. Spotlight still works; searching by the text in Spotlight shows a match, but clicking on the match (to open it in Mail) does nothing. I've tried rebuilding the mailbox and I've tried wiping the entire Mail directory; nothing works. Apparently other people have the same issue, but I haven't found a solution. This is too bad, because Mail.app is probably the most functional, no-nonsense client for macOS. I've tried some others (Airmail, Spark, Polymail, etc.), but they have a lot of usability issues and weird features (like Sparrow's team support) that are irrelevant to me.