I'm glad I'm not using this. It's the opposite of how I like to build web apps (which is either SSR with tiny bits of JS on top that I like to use Alpine.js for; or a JS-app that I like to use Elm for as life is too short runtime errors).
Nonetheless I hope all who do use Htmx, enjoy using it.
You can use ReScript with Htmx (or anything else) and get no runtime errors. It has a sound type system, great language.
I would classify HTMX as a different style of "SSR with tiny bits of JS on top." In fact, I would argue it is a more "pure" form of SSR-based interactive web development than an Alpine.js-style approach (I am not making any value judgment here).