hello! You may remember me from OnedriveMapper in the ~2017 - 2020 period (although technically it is still around, I'm happy to say it is dying 🙃)
As this forum was THE place people used / discussed it the most, I created an account at the time to better help people with OnedriveMapper, and remembered it just now for something else!
Because most of the people here are in EDU, I wanted to share with you that M365Permissions.com is (since recently) free* for ALL UK Public Schools.
M365Permissions.com is basically a tool that helps you identify oversharing in/outside your M365 tenant, it indexes ALL permissions even up to the mailbox folder or powerbi report level. Onenote, Power Automate, Azure, it includes it all and makes it searchable and analyzes it for 'bad' permissions e.g. doing Owner permissions for "Anonymous". (that's actually a real world example from a CEO's mailbox....you wouldn't believe it).
Because it has all this permission data, you can also use it for other things such as ISO certifications, audits, offboarding checks (unique permissions is really handy there). And the data is/stays yours and in your tenant, so anything else you can come up with...
Hope this helps you! And don't hesitate to shout out if I can improve anything
Cheers,
Jos.