Can I apply for a design patent if the internal structure also needs to be shown?

Let me start with the answer: No.

A design patent is a new design that is aesthetically pleasing and suitable for industrial application, based on the shape, pattern, or combination of a product, as well as the combination of color, shape, and pattern.

The main thing to protect is that the colors and patterns can be seen at a glance.

If the internal structure also needs to be protected, it is consistent with a utility model patent. A utility model usually refers to a new technical solution proposed for the shape, structure or combination of a product that is suitable for practical use.