Documentation

https://docs.python.org/3/library/subprocess.html#disabling-use-of-vfork-or-posix-spawn references

subprocess._USE_VFORK = False  # See CPython issue gh-NNNNNN.

subprocess._USE_POSIX_SPAWN = False  # See CPython issue gh-NNNNNN.

These are the only missing references I found in the whole docs.

I tried to find the correct issue number, however it was not as easy as expected:
It either is #80004 or #79718.