Sort the result of the main Query in shop page by a custom taxonomy

Question

In a WooCommerce site, we have products that have a custom taxonomy that are assign to a region.

When the user visits the site, we activate the browser geolocation, and we assign the user a region in a cookie.

Now we would like to show, in the shop page and in the product_cat taxonmies, in first the products that are assign to the same region of the user and then all other regions.

How could we implement this ?

So far, I taught of using pre_get_posts, and using something like :

add_action('pre_get_posts', 'order_by_region', 999999);
function order_by_region($q){
 if(!is_admin() && $q->is_main_query() && (is_shop() || is_tax('product_cat'))){
  $q->set('orderby', 'meta_value');
  $q->set('order', 'DESC');
  $q->set('value', $_COOKIE['nameofusercookie']);
  $q->set('meta_key', 'regions');

 }

 return $q;
}

But this didn't work. I just found that in there it will filter the posts instead of ordering by regions.

I found the 'the_posts' hook. That contains all the products after quering but not yet looped. I think it might be better place to sort all the products with the cookie. But how do i compare the cookie and the regions taxonomy in each products ?

add_filter('the_posts', 'sort_query_by_region', 10, 2);
function sort_query_by_region($posts, $q){
 $cookie = $_COOKIE['selected_region'];

 if(isset($cookie) && !empty($cookie)){
  if(!is_admin() && $q->is_main_query() && (is_shop() || is_tax('product_cat'))){
   $posts = sortByRegion($posts);
  }
 }
 return $posts;
}

function sortByRegion($posts){
 usort($posts, "regionOrder");
 return $posts;
}

function regionOrder($a, $b) {
   // get the cookie
   $cookie = $_COOKIE['slected_region'];

  // Get the term region of each compared product
  $regionA = get_the_terms($a->ID, 'regions')[0]->slug;
  $regionB = get_the_terms($b->ID, 'regions')[0]->slug;

  if($regionA != $cookie || $regionB != $cookie){
   return ($a, $b);
  } else {
   return $a < $b;
  }
}

I must that either doesn't work.

Anyone everdone such a re-ordering and knows I to help me?