> At a guess, the problem is because in atexit_callfuncs():
> 
>    module = PyState_FindModule(&atexitmodule);
>    if (module == NULL)
>        return;

In #31901, I solved this problem by getiing rid of PyState_FindModule in the atexit code, using module state and PEP-489 multiphase initialization.

This needed some changes in the pystate and pylifecycle code, so the specific interpreter has a reference to its own atexit module. This way, Py_EndInterpreter() is able to call the callbacks for the given interpreter.

See: https://github.com/python/cpython/pull/4611