Observable is geared toward the use of d3.js (essentially a library for drawing charts and graphs) which can be a bit intimidating, but you can use other libraries as well. For 3D, regl seems to be a good option. It's a library which makes using WebGL a bit more convenient. Here's an example of an Observable notebook that uses regl: https://observablehq.com/@rreusser/contour-plots-with-d3-reg...

Check out R. Reusser's other notebooks too. My guess is that choosing a set of JS libraries/tools to learn is the hard part, here, once you've committed to javascript.

http://regl.party/