How To Load an HTML File As A WordPress Page (With No 301/No Redirect)

You can use the template_include hook to accomplish this.

Add this to your active theme’s functions.php file (or create a plugin).

add_filter( 'template_include', 'wpse376643_load_html_page' );
function wpse376643_load_html_page( $template ) {
    if ( is_page( 'the-page' ) ) {
        // You'll have to use the server path to your index.html file.
        $template="/path/to/your/content/oct2020/index.html";
    }
    return $template;
}