At least on my machine and implicitly in [MNE-Python tests](https://github.com/mne-tools/mne-python/actions/runs/5421057815/jobs/9856038508?pr=11764): ``` >>> import joblib >>> with joblib.parallel_config('loky', n_jobs=2): ... print(joblib.Parallel(n_jobs=None).n_jobs) ... 1 >>> with joblib.parallel_config('loky', n_jobs=2): ... print(joblib.Parallel().n_jobs) ... 2 >>> joblib.__version__ '1.3.1' ``` No idea why it happens. On my machine it's from PyPI on Linux.