Document that milestones and labels are still available when issues are disabled
One confusing thing about labels and milestones is that they show up in navigation under the issues item. However, if you disable issues (or you can't access issues because you're not a project member) you may still be able to view the pages if you can access MRs.
This is deliberate: if you can see issues OR MRs (both of which use labels and milestones) then you shouldn't be denied access. They are missing from the UI which is annoying, but was backed up by research, and is a rare case anyway. (See #39268 (comment 50914570) for the UX research on this.)