An album used to shortlist pictures is an organisational view, not necessarily a separate set of image files. The same photograph can belong to several albums. When the shortlist changes, remove the album membership deliberately instead of deleting the photograph from the library.

Open the ordinary album you created in Photos on Mac. Confirm its name in the sidebar and select a single picture that should leave this shortlist. Avoid beginning with a large selection while you are still checking what the command does.

Use the album-specific removal command

Choose Image, Remove Photos from Album, reading the displayed item count. Apple documents that this removes the selected pictures from that album while leaving them in other albums in the library. If you chose the wrong item, use Edit, Undo promptly.

Return to the library and locate the same photograph using its date or visible content. If it also belongs to another ordinary album, check there too. This small test demonstrates the boundary between changing a collection and discarding its contents.

Continue tidying the shortlist only after the result is clear. When a confirmation uses wording about deleting photographs rather than removing them from the album, stop and reconsider the selection and command.

Retire the container when the project ends

If the whole ordinary album is no longer useful, Control-click it in the sidebar and choose Delete Album. Apple states that deleting the album leaves its photos and videos in the library. Preserve the album itself if its carefully chosen selection or sequence is still part of the project record.

This workflow concerns ordinary albums. Smart Albums and automatic collections gather items according to criteria, so their membership should not be managed by assuming the same manual-removal behaviour.

Finally, check the library rather than expecting album cleanup to reclaim the media’s storage. Removing an organisational container and deleting underlying photographs are different decisions. Make any actual deletion decision separately, with a checked backup and a clear understanding of which pictures are no longer needed.

References: Apple: creating and managing albums.