Here is the link to Yuneec’s Developer website https://developer.yuneec.com/?_ga=2.209018642.1652123650.1572912380-1638129901.1572912380. To my knowledge this is just applicable to the H520 which is Yuneec’s commercial platform. There was talk of third party support for the H Plus (same hardware as the H520) that never came to fruition, so if you are really wanting to develop on the Yuneec platform, the H520 is the only duck in the water at this time.
Maybe someone from Yuneec can confirm or deny this information.
Yes the main boards are slightly different. Have you contacted Yuneec about an SDK for the TH Plus? They will be the ones that can answer your query with any certainty. I’m sure that if there were an SDK published there would be more word available on the inter web.