SharePoint online has a data backup and restoration policy which for some users might be confusing. The following article will provide you a clarity to an extent.
In short a data can be restored within 108 days until unless it’s prematurely deleted by admin, in which case the data can be restore 14 days from premature deletion by admin.
User deleting a data:
When a user deletes a list item, or document library item or any site object, that deleted data is moved to a site’s recycle bin and stays there for 93 days or till user deletes it or site collection recycle bin quota exceeds.
User deleting a site recycle bin item:
When a user deletes an item from site recycle bin, that item is moved to site collections recycle bin. Only the site collection administrator will have access to this recycle bin. Here too the item stays there for 93 days from the date the user deleted it originally or till admin deletes it or site collection recycle bin quota exceeds.
Make a note that an item deleted by user will stay for 93 days regardless of it being there in site recycle bin (can be restored by user) or site collection recycle bin (can be restored by admin).
Admin deleting an item from site collection recycle bin/auto deletion:
Once an item is deleted from site collection recycle bin, it still can be restored if it’s available in the data backup by Microsoft
taken twice daily. Again this backup is available only for 14 days and SharePoint admin has to raise a support ticket.
When Microsoft restores the data, they will restore it as a whole site collection and not as individual item.