By default, we provide our Built-in Email builder only for global email types which come from WooCommerce directly but in some cases, if an extra plugin used good code practice and made their emails based on WooCommerce php class, actions, filters then it may work for them also.
Here is a topic where we described to one customer how to make it work from child-theme -> https://www.8theme.com/topic/built-in-email-builder-woo-subscription-email-templates-are-missing/#post-298316
+ We already added (ourself) most-popular questions from extra plugins to make them work with our Email builder -> https://prnt.sc/4eeZ-OIo2wQh
