No, you can’t remove the Inbox of a database. It is a core part of each database, regardless if you make use of it or not.
The only option is to disable Preferences > General > Sidebar: Unify inboxes, which will move the Inbox into the item list, similar to what was shown in DEVONthink 2.x.
However I dont know if there is a bug here because if I
Uncheck the unify inbox setting I get 1 unified inbox
If I check the Unify Inbox setting I get 7 separate inboxes.
That seems to be the wrong way around. However it has worked for me by unchecking the Unify Inbox setting it has unified my inboxes (if you get what I mean).
Uncheck the unify inbox setting I get 1 unified inbox
If I check the Unify Inbox setting I get 7 separate inboxes.
This is the correct behavior.
Unchecking the setting displays the Inboxes in their respective databases.
Checking the setting displays the Inboxes together (i.e., unified) in the Globals section.