Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi
If the subfolder was deleted in Classic Outlook, you may be able to recover it from the Deleted Items folder.
Open Deleted Items → find the deleted folder (or emails inside it) → right-click and choose Move Folder to restore it.
If it is not there, try Folder > Recover Deleted Items From Server (if your email provider supports it).
For more details, see: https://support.microsoft.com/office/recover-deleted-items-in-outlook-for-windows-0d4a9b1c-0d4d-4f1d-8e0d-4c5f6b6f6c9a
If the folder was permanently deleted or removed from the server, recovery may not be possible unless your email provider has a backup.