How can I save a selection of photos in darktable without copying the files?

darktable doesn’t have Lightroom-style “virtual collections” in the same way, but you can achieve the same result with ratings, color labels, and especially tags.

A common workflow is:

• rate your keepers with stars
• add tags to group related images
• filter the lighttable by those ratings/tags
• save that filter as a collection preset for quick recall later

For example, you could tag your 20 selected images with a project or trip tag, then filter by that tag whenever you want to see just that set. Ratings can also help, such as showing only 2+ star images.

If you want additional editable versions of the same image, darktable also supports virtual copies with Ctrl+D, but that’s for multiple versions of one photo rather than building a saved group.

So the closest equivalent to a saved selection is: tag or rate the photos you want, then use a saved collection/filter preset in lighttable.