How to create a private LAN for Mac hardware devices

Apple has long had robust networking support in macOS, allowing many different kinds of network interfaces to be connected at once, including multiples of the same kind (like ethernet), network adapters plugging into to interfaces (like ethernet over Thunderbolt and ethernet over USB-C), and multiple simultaneous internet connections.But Macworld reader Steven can’t get a particular installation to work that he needs for speed for his music recording studio. He has a 200Mbps internet conn