@BérangèreL, thanks for mentioning. You are correct according the info you already shared about the API.
@ymnagano, HubSpot has 2 ways of setting up a email. They have the drag and drop email editor. This is a nice feature for the user to create email templates without coding.
They also have the clasic editor for email. Here you can create custom template/modules for setting up emails.
If you want to migrate templates you have to use the clasic editor. It’s less user friendly for the user to manage or change. But it has options to import using CLI to create new files or using the API for Templates to create new templates.
The drag and drop email editor doesn’t have any export or import options. So that’s no option.