Can you give an example? OrbStack currently sets up an IPv4+6 interface linked to a "unified bridge" with both the macOS host and other Linux machines on it, plus NAT to the outside world: https://docs.orbstack.dev/machines/network

You're also free to create your own interfaces on the Linux side, of course.

You can have as many as you like, but you have to pass them as arguments in the VM configuration. It's not intuitive but the instructions are here:

https://github.com/utmapp/UTM/issues/2722