The site collection Recycle Bin exceeds its quota and starts purging the oldest items In that case, the items go to the site collection Recycle Bin, where they stay for the remainder of the 93 days unless: They stay in the site Recycle Bin the entire time, unless someone deletes them from there or empties that Recycle Bin. In SharePoint in Microsoft 365, items are retained for 93 days from the time you delete them from their original location. How long are deleted items kept in the Recycle Bin?

For info, see Restore a deleted site collection. If you're a global admin or SharePoint admin in Microsoft 365, you can also restore entire site collections from the site collection Recycle Bin. If you restore an item that was originally located in a deleted folder, the folder is recreated in its original location and the item is restored in that folder. Point to the items you want to restore, click the check icon to the right of each one, and then click Restore. If you don't see it, it might have been disabled or you don't have permission to access it. Note: You need administrator or owner permissions to use the site collection Recycle Bin.

Powershell empty recycle bin