I don’t see how the screen size is relevant at all. You can show any relevant portion of any UI/UX on any screen size you want. You can scale it down if you want, place it in a device mockup. Heck, you could even sketch a wireframe on paper and take a photo of it, if that sketch is solving a problem. Perhaps I’m misunderstanding your comment, but you seem to make the assumption that Dribbble is only meant for sharing desktop design at 1x. One look at the current front page shows that’s not the case.