Keep in mind that using beta version you participate ms insider program with all consequences (reporting a lot of data to ms etc.) :(

Official channel Outlook update is available now. Refer: 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