As @ROSEHAN says, 520 ships with the appropriate dongle (NEXT-1265WBTA, at least for my production run) in the box. You plug it into the USB port, and it allows WiFi and Bluetooth functionality in 520. Honestly, I am not sure if this was the best dongle choice, antenna is too big and heavy and the whole thing wiggles in the port, but it does work. If e.g. NEXT-531 also works, it might be better physically.
Now, the manual isn’t super clear that if you want to use a Bluetooth remote, a Bluetooth receiver needs to be installed, but… why would a dongle be included if it were built-in?..