def untag(self, value: dict[str, t.Any]) -> t.Any:
        """Convert a tagged representation back to the original type."""
        if len(value) != 1:
            return value

        key = next(iter(value))

        if key not in self.tags:
            return value

        return self.tags[key].to_python(value[key])
Convert a tagged representation back to the original type.
src/flask/json/tag.py