So before bothering trying to setup the generic or ffmpeg camera in Home Assistant I would download VLC and you can enter a network stream url there. I would test to verify you can reach the camera image at something like:
rtsp://<nvr-ip-address>:554/ch01/0
Make sure you can see the image there then begin setting up your first camera in ha using:
Or
Also you may want to try an app called NX-V to easily find your URL… it found a url for a camera that I struggled to find because it was locked down… although it may only find the first channel of your nvr but then you should be able to easily change to ch02 or ch03 for the others… it’s also possible that Onvif is disabled or not properly compatible at all if you don’t see any settings for the ONVIF port in your settings