Recommended online courses or other resources that cover designing 3d prints with moving parts

I've created a few prints with parts that snap together or print in place or rotate through each other, and have learned how to do so with a combination of random Youtube videos, reverse-engineering existing STLs with features that are interesting, and plenty of trial and error.

I'm wondering what resources other people use to learn to do this kind of stuff? Would love to learn about some more comprehensive sources of this kind of information, if such a thing exists.