How to parse shortcodes within returned content

Here's the code given by the VC team. And it works.

// display content in grid
add_filter( 'vc_grid_item_shortcodes', 'my_module_add_grid_shortcodes' );
function my_module_add_grid_shortcodes( $shortcodes ) {
$shortcodes['vc_post_content'] = array(
    'name' => __( 'Post content', 'fluidtopics' ),
    'base' => 'vc_post_content',
    'category' => __( 'Content', 'fluidtopics' ),
    'description' => __( 'Show current post content', 'fluidtopics' ),
    'post_type' => Vc_Grid_Item_Editor::postType(),
);

return $shortcodes;
}

add_shortcode( 'vc_post_content', 'vc_post_content_render' );
function vc_post_content_render() {
return '{{ do_shortcode_post_content }}';
}

add_filter( 'vc_gitem_template_attribute_do_shortcode_post_content', 'vc_gitem_template_attribute_do_shortcode_post_content', 10, 2 );

function vc_gitem_template_attribute_do_shortcode_post_content( $value, $data ) {
/**
 * @var null|Wp_Post $post ;
 * @var string $data ;
 */
extract( array_merge( array(
    'post' => null,
    'data' => '',
), $data ) );
$atts_extended = array();
parse_str( $data, $atts_extended );

WPBMap::addAllMappedShortcodes();

$output = do_shortcode( $post->post_content );
ob_start();
//  do_action( 'wp_enqueue_scripts' );
//  wp_print_styles();
//  wp_print_scripts();
//  wp_print_footer_scripts();
$output .= ob_get_clean();

return $output;
}

you could try do_shortcode() - Code Reference

add_shortcode( 'vc_post_content', 'vc_post_content_render' );
function vc_post_content_render() {
return do_shortcode('{{ post_data:post_content }}');
}

That should filter out the remaining shortcodes within the returned content.