Attached test works correctly on linux (3.7, 3.8) and mac (only 3.7).
Mac python3.8 falls with exception:

multiprocessing.pool.RemoteTraceback:
"""
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/multiprocessing/pool.py", line 125, in worker
    result = (True, func(*args, **kwds))
  File "test.py", line 8, in work
    print(F"Work={arg} args={args}")
NameError: name 'args' is not defined
"""

yeah this is normal. on Python 3.8 mac multiprocessing switched to spawn

you have to use https://docs.python.org/3/library/multiprocessing.shared_memory.html to share content between processes or pass it to be pickled in the args of imap_unordered

https://bugs.python.org/issue33725

Shared memory/pickle cannot send file descriptors

> Shared memory/pickle cannot send file descriptors

FYI Python 3.9 got new socket.send_fds() and socket.recv_fds() functions :-)
https://docs.python.org/dev/library/socket.html#socket.socket.send_fds

Can this issue be closed?  Multiprocessing seems to work as designed. There is a behaviour change between 3.7 and 3.8, but that's documented in What's New.