There are the API docs here (https://developer.garmin.com/connect-iq/api-docs/method_list.html) and you can search them, so far so good.
Question 1:
Is there a place where new API functions are announced? E.g. I just recently realised that oxygen saturation was exposed via API on many devices running API 3.2.0... I would like to know if i can check a place regularly to get this information and don't miss that.
Question 2:
I think I've read somewhere inside this forum that new values will be exposed via the next API generation in the future - is there any overview of this? Or is there at least a API documentation somewhere of the new SDK?