What what a magical tool! You can use this to scan your “My Drive” and “Shared Drives” (Team Drives) in Google to see what users files have been explicitly shared to.
After you scan you’ll get a big list of everyone that a file is shared with, including the ability to filter by users external to your organization. You can select an individual user and see what files are shared to them.
And it’s free
AMAZING! Find it at https://www.whohasaccess.com/
After you run the tool, I’d highly recommend revoking access to the to the app. Not that they would do anything nefarious, but why risk it? We’re good Admins 🙂