Same problem here. New MBP 14" with Monterey 12.0.1. Outlook search without any results. About to raise a ticket on MSFT, as Spotlight search finds emails, but not in Outlook, also tried rebuild of search and new Outlook Profile now good.

Switching to "New Outlook" resolved the issue for me, seach now works Outlook 16.55 (21111400) 1.0.1 Montery