Hello, most probably you are talking about .NET Standard
this page has information about which components support which version of .NET Standard
Latest Plesk Obsidian version ships .NET Core 2.2 version, which supports .NET Standard 2.0
There is no support of .NET Core 3.0 (which will support .NET Standard 2.1). No ETA at this moment.
In Plesk Onyx we are supporting .NET Core 2.0 so, this means that it is also supports .NET Standard 2.0.
If you are writing your application using traditional ASP.NET, then version 4.6.1 should be available as system component of Windows (which also supports .NET Standard 2.0).