Greetings Everyone,
I have a library and it has unique permissions. If a user who is not a part of the unique permission library sees the Site content of the site, he is able to see the library but when he clicks on it, he doesn’t see anything there and have no rights to add a new item or edit one which is fine enough.
My point is when he is not part of the permissions why can he see the library in all site content?
You may want to try executing “Check Permission” to see if the user has any permission granted.
It is in the Permission Setting page of the library.
Another thing to note is the Style Resource Readers group. This group by default is Everyone. You may want to remove this also.