I often saw mock-ups of unreleased or pure fantasy devices when I worked at Apple in Cupertino.

I often saw mock-ups of unreleased or pure fantasy devices when I worked at Apple in Cupertino. 

Usually, they were simple wood (or minimal function) boxes. Few were as polished as these designs by Rex Sowards.

https://www.designboom.com/design/what-if-apple-had-developed-pocket-macintosh-rex-sowards-05-05-2022/