Hello,
There are 2 places where I can see the configuration:
(1) in the project setting at the bottom (choose default assignee between project lead and unassigned).
(2) Automation page
I wanted to create an automation when an issue is created auto assign to one of my engineers but it takes into consideration only the default.
so I left it as unassigned and created the following rule:
When Issue Created
condition Issue is unassigned then assignee is XXX
My guess is that it is not working because the default one uses Unassigned with capital U and the Automation trigger uses with lower case.
This is hard coded by Jira.