Add a an action button in the Prestashop admin page header toolbar

MyAdminController.php

<?php

namespace MyModule\Controller;

use PrestaShopBundle\Controller\Admin\FrameworkBundleAdminController;

class MyAdminController extends FrameworkBundleAdminController
{
    // …
    
    public function indexAction()
    {
        // Here you can override some variables from the /src/PrestaShopBundle/Resources/views/Admin/layout.html.twig
        // template (layoutTitle, layoutHeaderToolbarBtn, layoutDisplayType, showContentHeader, headerTabContent, 
        // enableSidebar and help_link) by adding an associative array as second parameter of the render method.
        //
        // Seems to work from version 1.7.0.0.
        return $this->render('@Modules/mymodule/templates/admin/add.html.twig',[
            'layoutHeaderToolbarBtn' => [
                'add' => [
                    'href' => $this->generateUrl('admin_mymodule_add'),
                    'desc' => $this->trans('New block', 'Modules.MyModule.Admin'),
                    'icon' => 'add_circle_outline',
                ],
            ],
        ]);
    }
    
    // …
}