Cannot pass keyword arguments to QObject subclasses

following pattern works for PyQt6, but not for PySide.

from PySide6 import QtWidgets

class BasePlugin(QtWidgets.QStyledItemDelegate):
    _registry = {}

    def _init_subclass_(cls, identifier=None, **kwargs):
        super()._init_subclass_()
        if identifier is not None:
            cls._registry[identifier] = cls

class MyPlugin(BasePlugin, identifier="my_plugin_name"):
    pass

Error message:

TypeError: sbktype() takes at most 3 arguments (4 given)
make: *** [E:/dev/prettyqt/Makefile:38: test_pyside6] Error 4