This is the thing. Htmx is great if you only consider the frontend. But it does require fixing up the backed to match. A framework like that needs to integrate the front & back ends fairly tightly to have good UX. You may be interested in Datastar which does this better IMHO
I assume youre referring to the "starfield" on the home page. That's just showcasing their "Rocket" webcomponents tool, which makes it vastly simpler to make WCs.
It is otherwise a very simple website, and the framework and its SDKs are much simpler, yet more powerful, than HTMX
https://data-star.dev/