HTMX only does GET, doesn't to expo backoff, etc. Let alone the fact you need more extensions. Try it before claiming victory maybe?
The very top of the docs (https://htmx.org/docs/) shows how HTMX sends a POST request:
<button hx-post="/clicked"
hx-trigger="click"
hx-target="#parent-div"
hx-swap="outerHTML">
Click Me!
</button>