What is a share link?

A share link points at a file in Drive. Who can open it depends on how the file is shared, not on who has the link — so sending the address to somebody without access simply gets them a request-access screen rather than the file.

That is the safer default, and it is why sharing with a named person is more reliable than pasting a link and hoping.

Access can also be requested from that screen, which is often the quickest route when the owner forgot to include you.