The DJI HD system controller has a 3.5mm audio jack output.
This audio jack outputs PPM - so in theory this should connect like any other manufacturer transmitter (Spektrum / Futaba for example) to a simulator dongle.
Please make sure you update the firmware on the DJI controller before trying to connect it to a PC or a Mac.
For Mac use if you have USB Overdrive uninstall it as it can interfere with USB input from simulator dongles.
Choice of dongle is up to customers to try - DJI do not make any recommendations in this regard but any good quality simulator dongle should work (according to DJI).