Is there a way to show ‘all databases’ in the sidebar?
Databases can’t always be found in 'Recent Databases", even if you increase the ‘Recent items’ count in System Preferences, which I guess this keys off. The count of databases might be greater than the largest count option in the System Preferences, and/or you may not want every app to show so many recents.
You could add them to the favorites.
I did that and something seemed wrong, but I can’t remember what it was ! 
Anyway, thanks - I’ve done that again.
The trouble with making them all favourites is that you have two instances listed.
Suggestion: if a favourite is open, its listing in “Favorites” should be greyed out.
As unavailable favorites (e.g. databases on unmounted volumes or items in closed databases) are also grey it might be difficult to distinguish the two.
Ah, I didn’t know that. Oh well.