htmx glosses over the difficult part, which would be keeping track of the relationship between all these hx-post and hx-target attributes, when they're all just strings in markup. That glossing over is why you don't see any well-established backend libraries on the server integrations page. (https://htmx.org/server-examples/)

Elixir solves this in a much smarter way, because the bindings to reactive values can be validated at compile time, inside the HEEx templates. It's all located together, but you still get the diff passing behavior. (https://hexdocs.pm/phoenix_live_view/assigns-eex.html)