[2] If you look in Teams, some people have automatic permissions because they are in the Team or already have access to the Teams folder. If they are not in the Team, then you have to give "direct access".
[3] For the paranoid, you first go into OneDrive and "manage access". Then you are faced with two choices whose UX is confusing to say the least. One option is to "Copy Link" which has almost the same identical choices as "Share with Specific People". Note that "Share with Specific People" gives you options like "Anyone/doesn't require sign in" and the dialog has a button called "Copy Link". Huh? I thought I was sharing with specific people. I am still unsure who exactly can see the document. Or if the document was shared externally outside of my company.
SHAREPOINT https://support.microsoft.com/en-us/office/share-sharepoint-...
ONEDRIVE https://support.microsoft.com/en-us/office/share-onedrive-fi...