I have found that this file is used with _getGiftcardOptions()
vendor/magento/module-gift-card/Block/Sales/Order/Item/Renderer.php
that provides data to labels for gift card item in the Sales order confirmation email.
I am not much if there is any PHTML file that is also used with this process. As I am trying to update this gift card item data (i.e to add other product attributes as well in the email template) I need to override that template file.
Any thoughts on which template file is responsible for gift card products in email?