title: How to add meta boxes for custom post types with Wordpress gutenberg
body: <p>I'm trying to register a metabox for some custom post types. Currently, I'm using the add_meta_box function with the screen parameter set to the post type slug:</p>
  
  <pre><code>    $post_types = ['post', 'page', 'cms_pim_profile', 'cms_resource_hub', 'cms_stories', 'cms_opportunities', 'cms_events'];
      foreach ( $post_types as $post_type )
      {
          add_meta_box(
              'cms2019-sticky-until-' . $post_type,
              'Sticky',
              'cms2019_sticky_until',
              $post_type,
              'side',
              'high'
          );
      }
  </code></pre>
  
  <p>The problem is that the metabox simply does not appear for posts - the custom post types and the default 'post'. It does, however, correctly appear for pages, so I know the display/save functions are working correctly.</p>
  
  <p>Is there something else I need to do for posts?</p>