You are right, but it's possible to connect RS-422 to RS-232 using just proper wiring [1]. Basically, same three wires and one loop wire for RX+ to ground. It's not reliable and not recommended, but works and would solve the problem. :-)

1. https://stratusengineering.com/rs232-rs422485-conversion-cab...

The Mac RS-422 ports are backwards compatible with RS-232, dumb cables work fine. No Mac users were buying special RS-422 modems back in the day, we all used standard PC RS-232 modems and they worked fine with just a dumb cable. Even Apple's own serial printers were just RS-232.