In general we run a gstreamer command in cv2.VideoCapture(), as shown in this post:
V4l2src using OpenCV Gstreamer is not working in Jetson Xavier NX - #3 by DaneLLL

Please check steps in Jetson Nano FAQ
[Q: I have a USB camera. How can I launch it on Jetson Nano?]
and try to launch the camera in gst-launch-1.0 command. If it works in gst-launch-1.0 command, it should work fine by applying the command to cv2.VideoCapture().