Python (main.py):

import sys

from PySide6.QtCore import QObject, Slot
from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine, QmlElement

QML_IMPORT_NAME = "Example"
QML_IMPORT_MAJOR_VERSION = 1


@QmlElement
class Controller(QObject):
    def __init__(
        self,
        /,
        parent: QObject | None = None,
    ) -> None:
        super().__init__(parent)

    @Slot(name="testMethod", result=None)
    def test_method(self) -> None:
        print("test")

    @Slot(result=None)
    def test_method2(self) -> None:
        print("test")


def main() -> None:
    app = QGuiApplication(sys.argv)

    engine = QQmlApplicationEngine()
    engine.loadFromModule("Example", "Main")

    if not engine.rootObjects():
        sys.exit(-1)

    sys.exit(app.exec())


if __name__ == "__main__":
    main()

QML (Main.qml):

import QtQuick
import QtQuick.Controls
import Example

ApplicationWindow {
    visible: true

    Column {
        Button {
            text: "test"
            onClicked: Controller.testMethod()
        }

        Button {
            text: "test2"
            onClicked: Controller.test_method2()
        }
    }
}

With this example, calling Controller.testMethod() causes the application to crash, while Controller.test_method2() works.

The only difference between the two methods is that the first uses @Slot(name="testMethod", result=None) to expose the Python method under a different QML name.

Python: 3.14.2
PySide6: 6.11.2
Qt: 6.11.2
OS: Windows 11