cpython/Misc/NEWS.d/next/Core_and_Builtins/2024-11-23-04-54-42.gh-issue-127133.WMoJjF.rst

Calling :meth:`argparse.ArgumentParser.add_argument_group` on an argument group,
and calling :meth:`argparse.ArgumentParser.add_argument_group` or
:meth:`argparse.ArgumentParser.add_mutually_exclusive_group` on a mutually
exclusive group now raise exceptions. This nesting was never supported, often
failed to work correctly, and was unintentionally exposed through inheritance.
This functionality has been deprecated since Python 3.11.