Today, the state of the mac support in MvvmCross remains the same as before - as in MvvmCross for WPF and Xamarin.Mac: is it possible?
Yes, a few developers do successfully use it in MonoMac/Xamarin.Mac - but the project itself builds and releases binaries from Windows where there is no official support today for MonoMac or Xamarin.Mac.
For nuget, one developer has produced their own nuget packages for mac, but these are hard to use and maintain - as the Mac targets currently appear the same to nuget as the other x86 targets (WPF, console) - for some more on this see https://github.com/MvvmCross/MvvmCross/issues/502 (plus search other discussions there for "Mac" comments).
There is no official "Hello World" sample from MvvmCross for Mac - Mac is not as "first class" as the other platforms. There are some experiments included in https://github.com/MvvmCross/MvvmCross/tree/3.5/Samples/FirstDemo.Mac