keras/src/backend/numpy/trainer.py/NumpyTrainer/train_on_batch
class NumpyTrainer:    def train_on_batch(
        self,
        x,
        y=None,
        sample_weight=None,
        class_weight=None,
        return_dict=False,
    ):
        raise NotImplementedError(
            "train_on_batch not implemented for NumPy backend."
        )