Correct. The Xamarin API is 1:1 aligned with the native platform. To the point that it is almost entirely generated from automatic tooling with the odd "fix up" here and there.
Xamarin Forms however is a framework that performs abstraction, in a similar vein as React Native. Xamarin Forms is built upon the Xamarin API.
The great thing about Xamarin Forms is you can use Dependency Injection [1] to access the Native features.
I started with Xamarin Forms without any pre-knowledge of iOS or Android development. I use Xamarin Forms on a daily basis and share 99% of my code.
Is it on GitHub? I've been working with C# for a decade and will be getting into Xamarin now that it won't cost me thousands of dollars to do so. It would be great to have some Open Source examples to look at!
Xamarin Forms however is a framework that performs abstraction, in a similar vein as React Native. Xamarin Forms is built upon the Xamarin API.