Steps:

Restart Outlook and your computer.

Rebuild the Search Index:

Open Control Panel and go to Indexing Options.

Click on Advanced and then under the Index Settings tab, click on Rebuild.

Check Search Settings:

In Outlook, go to File > Options > Search and ensure that the search is set up to include all necessary data sources.

Check Connection:

Ensure you’re connected to the internet and that Outlook is connected to your Microsoft 365 account.

Update Outlook:

Check for any updates in File > Office Account > Update Options and click Update Now.