I have the OTG port connected to one of the four USB ports on a 4b. I'm not sure what the next steps are to get the actual connectivity to function, though. I've seen posts saying that gadget mode is only supported on the USB-C port - does that only mean for using the 4b as a peripheral, or does that mean for any connectivity, even if it's the host?
Well, uh, I hope your power supply can provide 3 Amperes.
Also you need to explain your network architecture. Does your Pi 4 connect to the internet using WiFi, and provides internet to Pi Zero? Your should see Pi Zero as USB-Ethernet card on your Pi 4, and you should be able to create a shared connection on this card from Pi 4 system settings if you connect a monitor and a mouse to your Pi 4.