I had the same issue after migrating to my new MBP M1 from a previous MBP core i9, both with macOS Monterey.
I tried to reindex the Main Profile folder, it works during the indexation and nothing after.
I tried to reindex the Macintosh HD disk with no more success.
I moved to the new Outlook and it works fine, all my mails are correctly indexed.
LTavel
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