Confluence works differently than Jira in case of licensed or not licensed users. Confluence itself restrict some functionality for unlicensed users, and there is no known workaround for this currently.
Licence Optimizer for Confluence should be configured as the Access group is added to the “Licensed users” Global Permission in Confluence administrator settings with “can use” enabled. This is the most basic permission that allows users to log in to this Confluence site. Users with this permission contribute to your licensed users count.
The problem is, that users that does not belong to any "can-use" permission are “invisible” for Confluence and some features that work with users are not available.
Some features are:
restricting space or page
mention a user
select in macro
etc.