I'm in favour of closing this issue.

If anything needs to be done its adding a warning to the documentation of os.fork() to the effect that doing substantial work in the child can be problematic on macOS. Maybe something like:

.. warning:: On macOS the child proces might crash if the parent
   proces uses higher level system APIs before calling this function. This
   includes, but is not limited to, using :mod:`urllib.request` in the parent
   process.