I think you are confusing the .NET Standard (ie. the standard to base implementations of .NET on) with .NET Framework which is going away.
http://gigi.nullneuron.net/gigilabs/wp-content/uploads/2017/...
The updated image is this:
https://devblogs.microsoft.com/dotnet/wp-content/uploads/sit...
Which seems to have removed the implementations (mono/.NET Framework) and implies .NET 5 will be targeted by all platforms directly?
So what is .NET Standard needed for anymore, platforms now target .NET 5 versions instead of .NET Standard versions right?