How to filter to specific folder collection and a custom header field

  items:  {
            '@taxonomy':
              {
                'numdep': '03'
              },
            '@page': '/others'
          }

---
title: test title
taxonomy:
    numdep: '03'
    insee: '03102'
geocoding:
  lat: 1
  lng: 2
process:
  twig: true
location:
    insee: 34129
    numdep: 34
---

public function onCollectionProcessed(Event $event)
{

    /** @var Collection $collection */
    $collection = $event['collection'];

    if ($infos = $this->isBarberDepartmentPage()) {

        $current_numdept = $infos['dept'];

        foreach ($collection as $item) {

            $numdept = $item->header()->location['numdep'];

            if (!empty($numdept) && $numdept != $current_numdept) {
                $collection->remove($item->path());
            }

        }
    }

}

 public function onCollectionProcessed(Event $event) {

    if ($this->isAdmin()) {

        $uri = $this->grav['uri'];

        if (isset($uri->paths()[1]) && $uri->paths()[1] === 'pages') {

            // $username = trim($this->grav['uri']->param('query'));

            /** @var Collection $collection */
            $collection = $event['collection'];

            $modify_user = 'just-for-test';

            foreach ($collection as $cpage) {

                if(!$cpage){
                    dump("An error has occured. Please contact site admin. No collection page found.");
                    continue;
                }
                $last_modified_by = property_exists($cpage->header(), 'draft') ? $cpage->header()->draft['last_modified_by'] : '';

                if ($last_modified_by !== $modify_user) {
                    $collection->remove($cpage);
                }
            }
            $event['collection'] = $collection;
        }
    }
}