Include custom theme blocks using the application api

I’m creating a Shopify App which redirects to an external domain to manage the service provided. Now, this service will create a few product views in an external domain, so I would like to create a custom block for the Shopify theme so that the user can add this theme block when he wants to have a carousel with links to those views.

Within the partners’ dashboard, I saw there is a theme section and apps section. What if I want an app that when installed, adds new custom blocks to their existing theme? Is that even possible?

I saw the API can create and modify pages, articles and comments, but there is no mention of blocks.

Sorry if this question is too basic, but I’m having this issue at the moment.