materio-d8/web/modules/custom/materio_expo/src/Controller/QRController.php

<?php

namespace Drupal\materio_expo\Controller;

use Drupal\Core\Controller\ControllerBase;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Drupal\Core\Url;

/**
 * Class QRController.
 */
class QRController extends ControllerBase {

  /**
   * Hello.
   *
   * @return string
   *   Return Hello string.
   */
  public function getfile($ref) {
    //? https://drupal.stackexchange.com/questions/255216/how-to-do-a-redirectresponse-with-a-destination-query-parameter

    //* get node from ref
    $entity_storage = \Drupal::entityTypeManager()->getStorage('node');
    $query = $entity_storage->getQuery()
      ->condition('type', 'materiau')
      ->condition('status', '1')
      ->condition('field_reference', $ref);
    $results = $query->execute();
    $nid = array_pop($results);
    $node = $entity_storage->load($nid);

    //* get file from node
    $file = $node->get('field_fiche_expo')->referencedEntities()[0];

    //* redirect to file
    return new RedirectResponse($file->createFileUrl());

    // return [
    //   '#type' => 'markup',
    //   '#markup' => $this->t("Implement method: getfile with parameter(s): $ref"),
    // ];
  }

}