Please take a look at the following article:
as mentioned in the article:
SharePoint Online retains backups of all content for 14 additional days beyond actual deletion. If content can not be restored via the Recycle Bin or Files Restore, an administrator can contact Microsoft Support to request a restore any time inside the 14 day window .
Note: Restorations from backups can only be completed for site collections or subsites, not for specific files, lists, or libraries. If you need to recover a specific item, find it in the Recycle Bin, right-click it, and choose Restore.