Sorry for the delay replying.

Steemit's github repo is here, and the API documentation is here. The API doc also contains tutorials for getting started in Python, Javascript, or Ruby... although they're getting dated at this point. A lot of the development activity went away after a controversial fork back in 2020, so we really still need to rebuild much of the ecosystem. It's a good time to get in at the ground floor, but it can also be challenging. Most of the interaction uses JSON, so you don't really need much specialized blockchain knowledge to work at the app layer.

As you can tell from my programming diaries posts, I'm far from expert, but glad to answer any question I can help with. I'll see if I can find track down some other articles that have been helpful. Maybe @moecki or @steemchiller can suggest resources, too.