LE Intermediate-Beginner wrote:

I realize saying it is still shutting down is not a very good clue. And of
course all the fumbling I did before this solution presented itself could be
causing the problem now.

How LONG before Outlook shuts down (which presumably means it exited and
outlook.exe is no longer listed in Task Manager's Processes tab)?
Doesn't seem like it could be an immediate exit if you had time to go
through the procedure to empty the Outbox folder of the stuck items.

Yet tried loading Outlook in its safe mode ("outlook.exe /safe") which
will not include any add-ons that you have installed for Outlook?