Collection in static function used by Admin blueprint does not contain pages

public static function getPageTitle($collection_options, $path)
    {

        $grav = Grav::instance();
        $l = $grav['log'];
        $l->info('Tutorial');
        $page = $grav['page'];
        $collection = $page->evaluate([$collection_options => $path]);
        $titles = [];

        foreach ($collection as $item) {
            $titles[$item->title()] = $item->title();
        }
        $l->info('Count: '.count($collection));
        $l->critical(print_r($titles, true));

        return $titles;
    }

      fields:
        content:
          fields:
            llocs:
              type: select
              label: Municipis
              data-options@: ['\Grav\Theme\Espurnes::getPageTitle', '@page.modular', '/qui-som/territori-barroc']

<?php
namespace Grav\Theme;

use Grav\Common\Grav;
use Grav\Common\Theme;

class Espurnes extends Theme
{
  public static function getSubscribedEvents()
  {
      return [
          'onThemeInitialized'    => ['onThemeInitialized', 0],
          'onTwigLoader'          => ['onTwigLoader', 0],
          'onTwigInitialized'     => ['onTwigInitialized', 0],
      ];
  }

  public function onThemeInitialized()
  {

  }

  // Add images to twig template paths to allow inclusion of SVG files
  public function onTwigLoader()
  {
      $theme_paths = Grav::instance()['locator']->findResources('theme://images');
      foreach($theme_paths as $images_path) {
          $this->grav['twig']->addPath($images_path, 'images');
      }
  }

  public function onTwigInitialized()
  {
      $twig = $this->grav['twig'];

      $form_class_variables = [
//            'form_outer_classes' => 'form-horizontal',
          'form_button_outer_classes' => 'button-wrapper',
          'form_button_classes' => 'btn',
          'form_errors_classes' => '',
          'form_field_outer_classes' => 'form-group',
          'form_field_outer_label_classes' => 'form-label-wrapper',
          'form_field_label_classes' => 'form-label',
//            'form_field_outer_data_classes' => 'col-9',
          'form_field_input_classes' => 'form-input',
          'form_field_textarea_classes' => 'form-input',
          'form_field_select_classes' => 'form-select',
          'form_field_radio_classes' => 'form-radio',
          'form_field_checkbox_classes' => 'form-checkbox',
      ];

      $twig->twig_vars = array_merge($twig->twig_vars, $form_class_variables);

  }

    public static function municipis()
    {
        $grav = Grav::instance();
        $pages = $grav['pages']->all()->ofType('espai');
        $collection = $pages->getCollection([
            'items' => [ '@page.children.visible' => '/qui-som/territori-barroc' ],
            'order' => ['by'=> 'lloc', 'dir'=> 'asc']
        ]);
        $logger = $grav['log'];
        $pages = $grav['page']->children();
        $logger->info('Children?');
        $logger->info('Count: '.count($pages));

        $dump = (object)['something'];
        $llocs = [];
        foreach ($pages as $page) {
            $dump[]=['something'=>$page->header()];
            array_push($llocs, $page->header()->lloc);
                /*$llocs[] = $page->header->lloc;
                $header = $page->header();
                if (isset($header->lloc)) {
                    $llocs[] = $header->lloc;
                }*/
        }

        $logger->critical('DUMP: ' . print_r($dump, true));
        $logger->critical('LLOCS: ' . print_r($llocs, true));

        return $llocs;
    }

    public static function getPageTitle($collection_options, $path)
    {

        $grav = Grav::instance();
        $l = $grav['log'];
        $l->info('Tutorial');
        $page = $grav['page'];
        $collection = $page->evaluate([$collection_options => $path]);
        $titles = [];

        foreach ($collection as $item) {
            $titles[$item->title()] = $item->title();
        }
        $l->info('Count: '.count($collection));
        $l->critical(print_r($titles, true));

        return $titles;
    }
}

$page->header()->lloc