How to sort posts in archive loop

by

This filter has to be set in functions.php.
Your filter won’t work as expected because your condition is wrong.
The condition here imply that you try to order pages (hierarchical post) instead of regular posts-like entries.

You have to be careful using this filter as it has effect on your whole website.

function my_custom_archive_order( $vars ) {
  if ( !is_admin() && isset($vars['post_type']) && $vars['post_type'] == 'pc' ) {
    $vars['orderby'] = 'menu_order';
    $vars['order'] = 'DESC'; // you probably don't need this because that's the default behaviour
  }

  return $vars;
}
add_filter( 'request', 'my_custom_archive_order');

https://codex.wordpress.org/Plugin_API/Filter_Reference/request