plone.classicui is a distribution for Plone 6.1 or later which comes with a basic Classic UI set of functionality.
This is similar to what you had when you installed the Plone package in Plone 6.0 and created a Classic UI Plone site.
The package does not contain page templates, it only contains dependencies to other add-ons and configures Plone. It can be used as an example for your own Classic UI based Plone distribution.