Possible no one has come across this issue. From the environment.yml script pip install opencv-python installs version 188.8.131.52. However this version that gets installed is for mac OS X 10.12. The error message at cv2 import reports that the libraries install are for OS X 10.12
As Apple machines of a certain age can’t upgrade to OS X 10.12 the version required for opencv-python is as follows
pip install opencv-python==184.108.40.206
I found this while trying the tutorials in the directory of that name under fastai. I use this box for simple experiments and fact finding. Yeah Apple what a web we weave!!!