Known Issue: Outlook search does not return results after upgrade to Windows 11
After upgrading to Windows 11, Outlook searches may return no result. This issue could happen with any account where the emails and other items are stored locally in PST or OST files such as POP and IMAP accounts. For Exchange and Microsoft 365 hosted accounts, this issue could affect offline search for the data in the locally stored OST files.
During the Windows upgrade, the search index is deleted and requires time to get rebuilt after the upgrade is complete.