Adding new parent item to admin bar

I don’t think you’ll need the parent for a root menu item while using add_menu. But make sure to get the hint in the Codex:

Note: The Admin Bar is replaced with the toolbar since WordPress
Version 3.3. The preferred way to add items to the toolbar is with
add_node().

Give it a try:

add_action( 'admin_bar_menu', 'toolbar_link_to_acf', 999 );

function toolbar_link_to_acf( $wp_admin_bar ) {
  $args = array(
    'id' => 'acf',
    'title' => 'Advanced Custom Fields',
    'href' => admin_url('edit.php?post_type=acf'),
    'meta' => array('class' => 'toolbar-acf')
  );

  $wp_admin_bar->add_node($args);
}