How to backup OneNote files that are in OneDrive

The gdoc and gsheet files are, as you've discovered, simply pointers to the online version(s) of the file(s). (This only happens if you have the Google Docs app on your PC or Mac, of course.)

The only way to make local backups of the files so that they contain your actual data would be to convert them to a different format. Converting a gdoc to a Word file and keeping it in the same directory would give you what you want, but converting files certainly isn't automatic.

Is it necessary, though? Google Drive/Docs is already keeping revision information, plus anything you delete goes to the "Trash" and doesn't get really deleted for 30 days (at least).

Of course, things might be a bit different for Google Apps. Certainly part of your agreement with Google is the ability to get to backups of your data in cases of vandalism/hacking/etc., no?

You might also look into the Data Liberation Front to see what data you can extract, although I don't know if that would be useful in your case.

I found Why is my account temporarily blocked from Microsoft Support.

Not exactly helpful but it does confirm that Microsoft are the ones asking for your mobile number (not some scammers). Still mystified as to why! Email would be a lot safer.