In Longform, a project can either be single-scene or multi-scene. A single-scene project is comprised of a single index file which is also the contents of your project. There are no additional notes (unlike in multi-scene projects, which have many scenes).
The idea is that this format is useful for (perhaps ironically) shorter-form projects, like short stories or essays. Projects you’d like to edit and compile within Longform but that don’t require a series of related notes.
These projects are available in the Longform pane like any other project, but do not have a Scenes tab.