Hello,
Inserting the example HTML from the x3dom tutorial works when using an Anvil custom component. So presumably there would be a way to save that HTML and use it on demand (hopefully a safe way).
I do not know what STEP, STP, etc, files are. It would be helpful if you added links to them. Or better yet, are you able to share a clone link with some sample images saved in a DataTable as media objects? This way others can play around to see if they can make them appear inside of a basic app.