How do I find which files were shared using an anonymous link?
Anonymous links are any open link created in OneDrive or SharePoint. These links act as an anonymous point of access into any file for which they are created. These pose a large risk to organizations’ information because it is impossible to see by whom they have been used.
To identify and investigate anonymous links, navigate to the “Investigation” tab and select “External Users” from the drop-down menu. “Anonymous users” will appear at the top of the user list."