The following static methods accept parent = None :

• QMessageBox.information
• QMessageBox.warning
• QMessageBox.critical
• QMessageBox.question

Example code :
QMessageBox.information(None, 'info', 'info')
QMessageBox.warning(None, 'warning', 'warning')
QMessageBox.critical(None, 'critical', 'critical')
QMessageBox.question(None, 'question', 'question')
QMessageBox.about(None, 'about', 'about')
QMessageBox.aboutQt(None, 'aboutQt')
 

It's not just a theorical issue. For example, I use QMessageBox.warning in my exception hook to display an better error message on Windows, but I don't have any QWidget instance at hand inside the exception hook.

Reported from PySide6-stubs

See full example : https://github.com/python-qt-tools/PySide6-stubs/blob/main/tests/qmessagebox.py