I actually really like using forms to submit to an iframe on the page. You can set the target attribute on a form to an id of iframe so on form submission, iframe gets reloaded.
It used to use HTTP 204's, but submitting the 204 made Firefox stop steaming the motion jpeg!? When I showed it off on HN in 2020, a PR was submitted that switched it to your iframe method which works smoothly in all browsers without JS.