Note that changing the os.fstat line to just "raise OSError()" no longer causes the "Fatal Python error", but rather gives the expected recursion exception.

Here's a shorter version that causes the fatal error in Windows native 3.9, cygwin 3.8.3, and Fedora Linux 3.7.7. So this isn't new with 3.9.

import os

def status():
    try:
        st = os.fstat(4)
    except status() as e:
        pass

status()