Allow tags and attributes in post and pages content

I am trying to allow the "onclick" attribute on links as well as some html tags such as iframe to the content displayed in posts and pages.

In my theme's functions.php file, I tried

• removing filters such as wpautop

  function rm_wpautop($content) {
    global $post;
    // Get the keys and values of the custom fields:
    $rmwpautop = get_post_meta($post-ID, 'wpautop', true);
    // Remove the filter
    remove_filter('the_content', 'wpautop');
    if ('false' === $rmwpautop) {
    } else {
      add_filter('the_content', 'wpautop');
    }
    return $content;
  }
  // Hook into the Plugin API
  
  add_filter('the_content', 'rm_wpautop', 9);
  

• adding tags

  add_action( 'init', 'allow_contenteditable' );
  function allow_contenteditable() {
    global $allowedposttags;
  
    $tags = array( 'iframe' );
    $new_attributes = array( 'contenteditable' = array() );
  
    foreach ( $tags as $tag ) {
      if ( isset( $allowedposttags[ $tag ] )  is_array( $allowedposttags[ $tag ] ) )
          $allowedposttags[ $tag ] = array_merge( $allowedposttags[ $tag ], $new_attributes );
    }
  }
  

without any success.