def _check_optimizable_historical_forecasts(
        self,
        forecast_horizon: int,
        retrain: Union[bool, int, Callable[..., bool]],
        show_warnings: bool,
    ) -> bool:
        """
        Historical forecast can be optimized only if `retrain=False` and `forecast_horizon <= model.output_chunk_length`
        (no auto-regression required).
        """
        return _check_optimizable_historical_forecasts_global_models(
            model=self,
            forecast_horizon=forecast_horizon,
            retrain=retrain,
            show_warnings=show_warnings,
            allow_autoregression=True,
        )

        Historical forecast can be optimized only if `retrain=False` and `forecast_horizon <= model.output_chunk_length`
        (no auto-regression required).
        
darts/models/forecasting/torch_forecasting_model.py