Yes, I used Mathematica to author https://quivergeometry.net, but I had to write the markdown converter, katex generator, rasterization caching etc. myself. Took a while to set up but works quite well now.

Some parts of it are quite flexible, like using Mathematica stylesheets to separate style and content for particular mathematical forms and change them globally to find the most ergonomic thing, with Katex that matches the mathematica (though I have to manually maintain that correspondence).

I do, and I consider jupyter to copy mathematica notebook, without seriously admitting it.