Why my jetson nano can't see the camera picture, but it can run successfully

Which camera you connected? Which JetPack version you used?
What’s the command you run?

Check with xvimagesink.

gst-launch-1.0 nvarguscamerasrc ! "video/x-raw(memory:NVMM), width=(int)1920, height=(int)1080,format=(string)NV12, framerate=(fraction)30/1" ! nvvidconv ! xvimagesink sync=false

I use a CSI camera and a DP port display.