These questions are always frustrating because there's two ways we can answer them neither of which you will like.
Think of the question instead as being.... "How do I paint a picture?"
Answer 1: By painting a picture
Answer 2: Using a canvas and paints and painting tools
You're asking how to make a piece of software. We can either tell you you make a piece of software by... making a piece of software or else we can tell you the tools and knowledge you will need to make that piece of software. Either way the answer isn't useful to you because the question itself is fundamentally flawed.
TL; DR - If you want a 6090 server you'll have to write a program that emulates the server functionality for that patch so that the client can connect and play. We're talking about tens or hundreds of thousands of lines of code to do it.
