separate each post type name by a comma (ex: ‘examples’, ‘snippets’)

function namespace_add_custom_types( $query ) {

  if( is_category() || is_tag() && empty( $query->query_vars[‘suppress_filters’] ) ) {

    $query->set( ‘post_type’, array(

     ‘post’, ‘nav_menu_item’, ‘examples’

        ));

      return $query;

    }

}

add_filter( ‘pre_get_posts’, ‘namespace_add_custom_types’ );

no need for a plugin!