Photos: View unassigned photos

Been years since I used an iPhone, and all of my photos were brought over from Android through the transfer app and organized into albums. I download a lot of photos, and will typically once a week come back and assign each photo to an album. However, I don't see a way to view unassigned photos so I can assign them to an album. I can't remember which ones were assigned, and all of the photos in the "recents" album and "Library" appear to be "all photos" (which seems to be redundant). Is there a way to distinguish between assigned and non-assigned photos? You would think if I clicked "add to album" on a photo that is already in an album, and scroll through the list it would have a check-mark or something indicating that it's already in that album, but it doesn't.

Very strange that the photos app has not changed since I used it back in the 3g era, you would think this app would have gotten tons of updates, new modes, new view types, new designs, etc. Seems crazy outdated and has barely any customization/organizational features.