In PowerPhotos (and any other third party app), you will always see the combined contents of both libraries when browsing through your photos. In Photos, you will see a menu at the top of the window that lets you switch between viewing just your personal library, just your shared library, or the contents of both libraries combined together. If you have the Shared Library feature enabled in Photos’ preferences, all of your photos will either be in your personal library (accessible to only you) or your shared library (accessible to other users who share the same library).
Starting in macOS 10.13 Ventura and iOS 16, Apple now offers the ability to have a Shared Library that allows multiple people to contribute to a single shared library that is synced via iCloud Photos to all of their devices.
