If Outlook search is mission critical, you can convert back to Big Sur providing you have a viable backup of your data. It would require considerable work as you would need to verify your backups, download Big Sur, burn a USB thumb drive with the Big Sur installer and then completely erase the internal disk and re-install Big Sur, update it. Then restore your data from backup and re-install all your software.
How to download an older version of macOS
https://support.apple.com/en-us/HT211683
How to create a bootable installer for macOS
https://support.apple.com/en-us/HT201372
Or you can wait for Microsoft / Apple to fix the problem with Outlook Search on macOS Monterey 12.1. Now that the holiday season is coming to a close, there should be some updates coming soon. Be sure you file a bug report with Apple and Microsoft.
Apple Feedback Assistant
https://feedbackassistant.apple.com
Microsoft Outlook
Help menu -> Give Feedback to Microsoft