Remove ALL HTML from single page

You could make a template for this in your active theme, then assign that page to use the new template file.

null-template.php

<?php
/**
 * Template Name: Null
 */
 
if ( have_posts() ) {
    while ( have_posts() ) {
        the_post();
        the_title();
        echo( wp_strip_all_tags( get_the_content() ) );
    }
}

Then create a new page (or edit the one you want to be HTML-free) and make sure it’s using the Null template.

This should result in a page that has no HTML whatever in it.

References

• Template files
• wp_strip_all_tags() for when you really don’t want any tags left behind