This is essentially a recurrence of #604, but affecting a recently released Python version: 3.12.1. See python/cpython#112826. I merged a workaround in CPython for 3.12 (to preserve compatibility with 3.12.0), but for 3.13+ this will need to be fixed in eventlet.

Basically, eventlet/eventlet/green/thread.py needs something like the following added:

_is_main_interpreter = __thread._is_main_interpreter

I'm happy to open a PR if that would help.