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<?php
include_once(dirname(__FILE__) . '../../../mymodule.php');

class myModuleDefaultModuleFrontController extends ModuleFrontController
{
    public function __construct()
    {
        parent::__construct();

        $this->context = Context::getContext();
    }

    public function initContent()
    {
        parent::initContent();

        if(isset($_POST['take_data']))
        {
//HANDLE THE POST  HERE
 			$product_ID = $_POST['product_ID'];
            $ID_product_attribute = $_POST['ID_product_attribute'];
/* action */

/* when job done then redirect */

            $openTab = 3;

          // $pController  = $this->context->link->getAdminLink('AdminProducts', true, ['id_product' => $product_ID]);
          // $pController .= '#tab-step'.$openTab;

			$link = $this->context->link;
            $url = $link->getAdminLink('AdminProducts', true, array(
                'route' => 'admin_product_catalog'

            ));
            $url.= '#tab-step'.$openTab;
       
     /* i have tried also:
$url =  $link->getAdminLink('AdminOrders', true, [], ['orderId' => 44, 'vieworder' => 1]);
*/

		/*that works */
          //  Tools::redirect('index.php');

            }

    }
}

Sure here is myModule front controller. Actions are fine - I have problem with getAdminLink() - probably some stupid mistake.