I'm sorry, I'm still not getting it.
Right now, in order for editors to be able to access the Media Libraries App at all, they need to be give access to Media libraries, Edit media library, and Files within "UI Personalization".
However, these settings override the security settings of the individual Media Libraries, so any user can access any library regardless of which department they are in. Even if the security access is set to Nobody!
How do I give a role access to only one Media Library?