Have you read the book ‘Flatland’ by Edwin A Abbot? What a romantic dive into one-, two- and three-dimensional thinking. Whenever I see shadows, I think of Flatland. In Flatland, a 2D (two dimension) object would cast a 1D shadow onto a 1D world. For example, a circle would only have a dot as a shadow from any vantage point in the 1D world.
In a 2D world, a 3D object, for example a Sphere, would cast a 2D shadow (a circle) in the 2D world. The same principle applies to the tree in my front yard. Our tree is a 3D object. Yet its shadow is 2D on the flat 2D surface of my driveway.
Now for the fun part. A 4D object would cast a 3D shadow (our 3D tree.) What would our 4D tree look like given its 3D counterpart?