I’m on Windows and using a RME Fireface UFX+ interface and RMEs TotalMixFX software to route audio. Just route your signals you want to send to zoom (main out Nuendo, Talkback, etc…) to a bus, which then is selected as your input device in Windows sound preferences. Zoom, Skype, Slack, etc… are using the standard Windows input here on my machine. Easy as that. Should work similar with every other audio interface.
You can also create different outputs directly in Nuendo and work for e.g. with direct routing to route your signals to a specific bus on your audio interface. Then choose this bus as the input source in zoom.
All the best