According to this StackOverflow question, one can use the
public void ActivatorNotAbstract()
var activatorType = typeof(Activator);
The issue here is you assumed the following:
although System.Activator is defined as a static class
Interestingly, this is technically correct since the library you compile against defines
System.Activator as a static class. This can for example be seen at the source code of the System.Runtime reference assembly or the in a part of the
netstandard.dll reference assembly source code.
However, these libraries are meant as a compile-type interface and the actual runtime implementation may derivate a little from this declaration.
In fact, both .NET Core and .NET Framework implement the class as
public sealed class Activator (.NET Core) or
public sealed class Activator : _Activator (.NET Framework).
This implementation causes
IsAbstract to return