There is no default database any longer - except the Global Inbox. Also, any databases that were open when you quit DEVONthink will reopen on the next launch.
I set my DEVONthink > Preferences > Import > Destination to Select Group. When I import something, or drag it to the dock icon to import or index, or use the DEVONthink PDF Service to print a PDF to a database, this setting causes the group selector to open, and I then choose the database-and-group destination I want. Group selector remembers this setting for each import until I change it. So, in that sense, this creates a “default” destination, on the fly, that is persistent until I reconfigure it.
Very flexible, in my option, and better than dumping everything into the Global Inbox or the inbox of some other database – a choice (in my case) that is always not what I want.
In Devonthink to Go, however, when creating through force touch a new note, there I cannot find an option to direct my newly created note any place else than the default (!) Global Inbox.
Personally speaking, no. If I was just jotting a quick note, I wouldn’t be thinking about where to file it. I just want to capture something quickly and sort it out later. That’s what the Global Inbox is made for.
If I was in need of filing the note somewhere specifically, I’d go into DTTG and make the note where it needs to live, again speaking from my personal habits and point of view.