So, python3-joblib doesn't always fail to install. It installs fine for the statsmodels [1] and scikit-learn [1] autopkgtests against python3-defaults 3.9.0-3.
[1] https://ci.debian.net/packages/s/statsmodels/testing/amd64/ [2] https://ci.debian.net/packages/s/scikit-learn/testing/amd64/
