Is there a way to build APIs for Apple Freeform?

APIs for services are technically built by the service provider, in the case of Freeform, the API would need to be built by Apple to allow access to the Freeform platform from other applications or platforms.

https://www.mulesoft.com/resources/api/what-is-an-api#:~:text=API%20is%20the%20acronym%20for,APIs%20are%20all%20around%20us.

With that said, not sure what an API would do for Freeform.

Freeform is a collection of items in a somewhat organized manner. But an API or any other platform connecting to it would not see the board used for Freeform, it would just see a list of files.

I guess it could be used to display a Freeform project somewhere else, but I doubt Apple is prepared to allow that at this time.

Unlikely Apple would ever expose the Freeform platform for connections like that.