Usually the Taranis should be plug and play on macOS. Make sure you don't have any other controllers/joysticks/tablets connected, that might cause a conflict. Also, if you have installed some kind of custom USB driver such as USB overdrive, that might be something worth looking into.
Hey,
Everything works with my Turnigy i6s so the set up is good, and you don't really need a USB dongle with Taranis radios because of the mini-USB port, it's automatically recognized as an HID device. It's detected by my Mac and works great with other software asking you which input controller you want to use (crrcsim for example). Freerider just doesn't seem to want to choose it, it's weird…