I installed a fresh Microsoft Visual Studio on my laptop and installed Xamarin as well, started a new project and just tried running.
But I cannot run, it is giving me an error message that says….

The Current .NET SDK Does Not Support Target .NET Standard 2.0. Either target .Net Standard 1.6 or lower, or use a version of the .NET SDK that suports .Net Standard 2.0

This error means what it says; mis-match in SDK .NET version and the emulator .net version.

This vlog demonstrates how I resolved this problem.