There is nothing I can think of that would cause a USB issue with a specific macOS version, so I am not sure why the USB audio would be working on your older computer and not the newer one. A few things you can check:
– Are you using the same USB cable for both computers? Have you tried a different USB cable with the computer that isn’t working?
– Are you using a USB hub or extender with the computer that isn’t working?
– Are you using Direct I/O connections? Or is audio going through an FX Chain?
– How are you troubleshooting your audio setup? Can you try loading an Oscillator algorithm and seeing if it outputs on the USB channels?