I can confirm this runs fine on 1.12.1. The installation is recommended in the other thread will update your version to 1.13.1 (which I checked as well, and it works).
Could you perhaps try running this modified code to see if you get an output:
from depthai_sdk import OakCamera
with OakCamera(replay='https://www.youtube.com/watch?v=Y1jTEyb3wiI') as oak:
color = oak.create_camera('color')
nn = oak.create_nn('vehicle-detection-0202', color)
oak.visualize(nn, scale=2 / 3, fps=True, callback=lambda frame: print(frame.detections))
This should be printing out all detections on a frame, without actually showing the frame. Perhaps there is a problem with opencv on your cm4.