Scan your WordPress content for (anything) a URL and then insert some prefetch hint etc into the head element.

functions.php

function prefix_filter_embeds( $content ) {
  if strpos( $content, 'string' ) !== false ) {
    add_action( 'wp_head', 'prefix_url_actions', 0 );
  }
  return $content;
}

add_filter( 'the_content', 'prefix_filter_embeds' );

function prefix_url_actions() {
  echo '<link rel="prefetch" href="" crossorigin>';
}