title: Is it possible to use C# 9 for Xamarin?
body: <p>Officially, C# 9 only supports .NET 5. What about Xamarin? Is there an unofficial way to use C# 9 in Xamarin? What about libraries? Does it mean that any library that wants to support Xamarin cannot use C# 9?</p>
  <p>EDIT:</p>
  <ul>
  <li>What are the recommended practices for library developers to use C# 9 and support Xamarin?</li>
  <li>Does Xamarin enabled libraries should target .NET Standard 2.1?</li>
  <li>What features of C# 9 are not available to Xamarin { Android / iOS } / .NET Standard 2.1 / .NET Framework (legacy)?</li>
  </ul>