How to enable USB communication between AGX and NX

Hi,
There is only one port which can run in device mode. If you have proper design on the custom board, you can refer to adaptation guide to modify device tree and change to USB2-1 port.

For RNDIS_HOST, do you mean USB tethering? There is an issue about it on r32.3.1:
Android USB tethering not working - #28 by DaneLLL
It is fixed in latest r32.5.1.