Creating a shared iCloud Photo Library for duplicate photos

léonie is the expert on this Share Library for Yourself thing, and I've not done it. But, until she checks in, you should see this:

Things to consider when setting up the Shared iCloud Photos Library in Photo 8 on Ventura

Don't be put off by the "on Ventura" thing-- it's where Shared Libraries were introduced.

Strictly speaking, the photos in the main library aren't duplicates; they are the actual photos. The photos "in" the albums just are just pointers to them. That's why deleting them or hiding them from the library deletes or hides them in the albums. However, they do appear to be duplicates, so I understand your question.

There is a way you could achieve something somewhat like what you want using your (one and only) Shared Photo Library, but it would be manual and cumbersome, and it would not be useful for actual sharing. It would work something like this:

When you add photos to albums, also add them to your Shared Library.

When you want to view your library without those photos, set the view to Private Library only.

When you want to view your albums with those photos, set the view to Shared Library or Both Libraries.

Another approach would be to define a Smart Album with criterion ("Album", "is not", "Any") and view that Smart Album (instead of the Library) when you want to see what hasn't been added to any album.

What I've been able to determine is if a photo is hidden it is hidden from anywhere in the library, albums and smart albums, except for projects. This is on Sequoia.