The Photo Mechanic Plus interface is divided between the Navigator and the Organizer. The Navigator area looks and behaves like Photo Mechanic 6.  The Organizer is where you can access your catalogs and collections.
On macOS, find the Organizer here:

On Windows, find it here:

The Organizer allows you to find, filter, and browse through your catalogs. The main areas for the Organizer view are: