When you delete content from a SharePoint site, it's sent to the site's Recycle Bin or first-stage Recycle Bin, where you can restore the deleted content if needed. Unless someone deletes content from a site Recycle Bin, it's never sent to the site collection or second-stage Recycle Bin.The SharePoint site collection administrator can view and restore a user's deleted item from the second-stage or Site Collection Recycle Bin to its original location. If an item is deleted from the second-stage Recycle Bin, or it exceeds the retention time, it is permanently deleted. For more info, see How long are deleted items kept in the Recycle Bin?
In SharePoint Online, the default retention time is 93 days for both site recycle bin (first stage) and site collection recycle bin (second stage). The site recycle bin storage counts against your site collection storage quota and the List View Threshold. The site collection recycle bin retention starts at the same time for both recycle bins when the item is first deleted, so the total maximum retention time is 93 days for both recycle bins. The amount of space allocated to the site collection recycle bin is 200% of the site collection quota. These values are not configurable.