Same issue here on my Intel 13" MBP. I simply upgraded, and even with 12.1 I'm seeing the same issue. I can find emails by subject that existed prior to the upgrade but not after. I tried the same Spotlight workaround from past OS versions. Oddly enough if I search using the subject for emails that I received post 12.1 upgrade in FINDER I can find them, but not in Outlook search.

That's MS's published workaround. The "New Outlook" does not support Local Folders though, so once you make the switch you loose any local mail, which for me is about 10 years worth of extremely important emails. https://support.microsoft.com/en-us/office/search-in-outlook-for-mac-returns-no-results-after-installing-macos-monterey-12-1-075c5f09-35db-4205-aba3-eea2f168c71b