@glemaitre
I think I see where the error is. In this rendered file,
https://147552-843222-gh.circle-artifacts.com/0/doc/modules/generated/sklearn.multioutput.MultiOutputClassifier.html

It gets rendered as:
property predict_proba

But, I am not sure where/how to fix it. It's line 412 here:

    @property
    def predict_proba(self):
        """Probability estimates.
        Returns prediction probabilities for each class of each output.

        This method will raise a ``ValueError`` if any of the
        estimators do not have ``predict_proba``.

The property bad rendering should not be the issue. It is indeed not a nice rendering but the introduction of available_if instead of the property will solve this rendering issue (e.g. #20667)

Should I be commenting out all 4 of these in test_docstrings.py? Currently, I have just commented out ClassifierChain.

__all__ = [
    "MultiOutputRegressor",
    "MultiOutputClassifier",
    "ClassifierChain",
    "RegressorChain",
]

Yes if you are modifying the docstring of the other estimators, you can uncomment. I can update the title.

Since I merged yesterday the docstring for ClassifierChain, I merged main in the branch and uncommented for the MultiOutput* estimator and RegressorChain. It was passing locally so I think that everything is fine. Let see if the CIs will agree.

Thanks @reshamas