eliminate all photos not belonging to an album

Hi all,

I just recently realized that Photos works as a database and that when I eliminate photos from an album, it's not the photo but the reference that gets erased.

That means that, on top of the photos I want to keep, somewhere in my library I have a lot of photos I had decided to erase but are still somewhere.

For example, when I import photos from my iPhone, I tend to import every new picture or video and then sort what I want to keep in albums, erasing the rest. However, the photos I wanted to eliminate are still in the Import folder.

I saw that, in earlier versions of the Photos app, you could create an intelligent album with the photos not belonging to an album like this:

1. Choose File > New Smart Album.
2. Select from criteria Album, Is Not, Any.
3. Name and click OK.

and then erase them from there, but that does not seem to be the case anymore (can't find the Any option and the rest are not relevant for what I want to achieve).

Does someone have a suggestion?

Thanks,

Alex