Using older versions of Outlook for Mac for personal email and calendar
Hi yobelow,
In this situation, you can try to create a new Outlook profile and check if the issue persists in the new created profile.
Note: Do not remove the old profile.
In addition, according to my research, I found a known issue that Search doesn't work in Outlook for Mac after MacOS upgrade. And the status is INVESTIGATING.
Here is the article for your reference: https://support.office.com/en-ie/article/search-doesn-t-work-in-outlook-for-mac-after-macos-upgrade-b73de6f1-aeb9-4720-bbbe-de65ab50012e
Best Regards,
Huni