If a database isn’t open, its name is shown in italic type in the Navigate sidebar. This should be the case in both the Favorites and Recent Databases, e.g.,…
File Types is open.
Automation is not.
Note: Active Issues is in grey since the database isn’t in its expected location in the Finder. If I move the database back to its original location and reopen the Navigate sidebar, it would appear in black type. The database can actually still be opened with a double-click in this state, but will remain greyed. @cgrunenberg would have to comment on if it should change appearance (and perhaps update its file path, though I don’t know the technical details here).