Somewhat disappointing that it's just a console app. I'd love to be able to do cross platform C# desktop development. There shock be something equivalent to WinForms/WPF on OSs other than Windows.
There won't be a Forms or WPF port.
But it sounds like you are actually thinking of Xamarin.Forms, which allows sharing UI code on mobile platforms as well as UWP. You are correct that there is no Mac support for that.
Xamarin.Mac provides C# bindings to Mac desktop APIs, and has nothing to do with Xamarin.Forms.