There isn’t a feature like what you describe. “Done” is not a concept that the app has – it has no way of knowing when you are done with an edit. Conceivably the app could provide a way to set up a folder or Photo library album that you can quickly move files to (via a shortcut key). Have you seen such a feature in other apps? As far as a “edits since last export” goes, it’s certainly possible, but it’s fragile. You could be working on a project and then have to quickly output a unrelated file for someone and the flag has been reset.