Years ago, after Xbox live for the original Xbox shut down, there was a program you could run on your PC that would connect to others running that software.

It would emulate a local Xbox and do matchmaking and your local Xbox would see the others as “local” using the system link option for multiplayer games (Halo, etc)

For the life of me I cannot remember what that was called, and my Google-fu is failing and only returning results for console emulators.