If you have problems searching in subfolders, please do the following:
\uD83D\uDCD8 Instructions
Open Outlook 365
Click “File”
Click “Account settings”
Choose “Account Name and Sync Settings”
Click on “More Settings”
Navigate to the advanced tab
Remove the checkmark from “Download shared folders”
Press “OK”
Remember to restart Outlook after this change.
Please note that mails in shared mailboxes may disappear. Please give Outlook some time to fetch these mails from the server.