I experience the same, and I think it's the MacOS and not Outlook causing the problem, because it stopped responding to my searches the same day I installed Monterey, October 25th 2021. I have tried "everything", including reinstalling Monterey (12.1) without a positive result. I have to use Mail in parallel to search in my 37.000 mails in one of several inboxes and 2.500 contact records. I hope Mac developers take this seriously now!!