First check that your CSI camera can be read from Argus in gstreamer:
gst-launch-1.0 -v nvarguscamerasrc ! 'video/x-raw(memory:NVMM), width=640, height=480, framerate=30/1' ! nvvidconv ! xvimagesink
This assumes you have a gui running with local display or through ssh with X forwarding. If you can’t see the camera feed, post the ouput of this command.
If ok, you may also post the ouput of these python commands for checking that your opencv version has gstreamer support:
import cv2
print(cv2.getBuildInformation())