If you want to open a new window when you click on the button & use the empty layout in it then you have to follow the below steps.

Step 1: Place a new button in the admin and you have to make the on-click as per the below code.

$this->setChild(
    'add_print_button',
    $this->getLayout()->createBlock('MagentoBackendBlockWidgetButton')->setData(
        [
            'label'     => __('Print Registry'),
            'onclick'   => "window.open('".$printUrl."','_blank', 'toolbar=yes,scrollbars=yes,resizable=yes')",
            'class'     => 'task action-primary registry-print',
        ]
    )
);

Step 2: Now in your controller you have to copy-paste the below code in the execute method to display your content in the empty layout.

/** @var MagentoBackendModelViewResultPage $resultPage */
$resultPage = $this->resultFactory->create(ResultFactory::TYPE_PAGE);

$registryId = $this->getRequest()->getParam('registry_id');
$registry = $this->registryFactory->create()->load($registryId);
$items = $this->getPrintItems($registryId);

$resultPage->addHandle('admin-empty');
$this->_addContent($resultPage->getLayout()->createBlock('MirasvitGiftrBlockMailPrintitems')->setRegistry($registry)->setPrintItems($items));

return $resultPage;

That’s it. Now I can see content in the empty layout page in the Magento admin side by clicking the button.

Note: This code is designed as per our requirement. You can modify it as per your requirements.