Ed is blind and has trouble controlling his HAM radio with his computer. Leo says if he has software that is designed to control it, and a cable that converts USB to RS232, then it should work. The chatroom says that they haven't gotten it to work on Macs either. Macs don't work because they don't recognize COM ports. Windows, by contrast, is backwards compatible and has support for that. He'll also need drivers. If the COM port adapter came with software, then that could also be the issue.
Mike's PBX Cookbook has drivers and terminal commands that might make it possible for Ed's Mac to recognize a COM port.