Sharepoint offers a way for a site owner to see how the site is being used and what items have been shared out with different users.
While viewing your Sharepoint site, click on Site Contents on the left-hand side.
Click on the "Site Usage" button on the toolbar. This will then show various metrics about your Sharepoint site.
Scroll to the bottom of the page, click the link under Shared with External Users called Run Report
Depending on how many files and folders are in the site, this process could take a while
Choose a location within your Sharepoint site and click Save to save the report
Once the report is done processing, there will be a CSV file with the name of the Sharepoint site and the date and time it finished processing, in the folder you chose. You should also receive an email with a link to the report location.
If you do not see one, check your spam folder
The report will show the folders, who has what access and individual link IDs.