Pass argument to custom access callback
Your route:

regportal_user.orders:
  path: '/user/{user}/orders'
  defaults:
    _entity_view: 'user.orders'
    _title: 'Управление заказами'
  requirements:
    _custom_access: '\Drupal\regportal_user\Controller\RegportalUserController::accessOwnOrders'


Your controller:

  /**
   * Checks access for a regportal_user.orders route.
   *
   * @param \Drupal\Core\Session\AccountInterface $account
   *   Run access checks for this account.
   *
   * @return \Drupal\Core\Access\AccessResult
   */
  public function accessOwnOrders(AccountInterface $account, $user) {
    if ($account-&gt;id() == $user) {
      return AccessResult::allowed();
    }

    return AccessResult::forbidden();
  }