I do software FX on my guitar using my Mac and a USB interface, but the produced output sound goes back to the interface - I can listen to it but I can't record it on my Mac, only the input sound device pre-FX.
I'm aware of "virtual cables" and "virtual sound cards" but I understand Windows for instance can allow direct capture of a sound-card output.
Is this something available on macOS and if so, which versions - and any general information I should know?

avfoundationis the API and macOS doesn’t give you access to drivers or the hardware directly. Windows doesn’t allow you do access the hardware or drivers directly either. You have to go through the HAL (hardware abstraction layer) – Allan May 12 '20 at 17:40avfoundationis would complete this answer, then @Allan. Particularly, given I have multiple audio devices, how your example selects which output it 'listens to. – Mr. Boy May 12 '20 at 19:14