aboutQt = QtWidgets.QMessageBox(dialogWindow(ui.ui_aboutQt.Ui_Dialog))

creates an anonymous QDialog temporarily, makes the QMessageBox have that to center on, and then destroys the QDialog so the message box now is to be centered on a non-existent dialog? Might cause the message?

aboutQt.aboutQt(aboutQt)

don't know what this would do, seems to pass aboutQt to center on itself? Might cause the message?

The method is static aboutQt(parent[, title=""]). So it's static, and I believe it creates and displays the whole "About" dialog. Don't know what your intention to create your own about dialog is about? (If you want to display some dialog of your own as the parent for the aboutQt message box you need to create and show that dialog and keep a reference to it.)

I thought you were just supposed to write something like:

QtWidgets.QMessageBox.aboutQt(None)

No instances of anything. No dialog of your own.

To center that on the main window, if you want that, you would pass your window = mainWindow() instance as parent.

P.S.
I see there is also a convenience QApplication.aboutQt() method. So app.aboutQt() should also work.

I thought you were just supposed to write something like:

QtWidgets.QMessageBox.aboutQt(None)

This works perfectly, thank you

aboutQt = QtWidgets.QMessageBox(dialogWindow(ui.ui_aboutQt.Ui_Dialog))

creates an anonymous QDialog temporarily, makes the QMessageBox have that to center on, and then destroys the QDialog so the message box now is to be centered on a non-existent dialog? Might cause the message?

aboutQt.aboutQt(aboutQt)

don't know what this would do, seems to pass aboutQt to center on itself? Might cause the message?

The method is static aboutQt(parent[, title=""]). So it's static, and I believe it creates and displays the whole "About" dialog. Don't know what your intention to create your own about dialog is about? (If you want to display some dialog of your own as the parent for the aboutQt message box you need to create and show that dialog and keep a reference to it.)

I thought you were just supposed to write something like:

QtWidgets.QMessageBox.aboutQt(None)

No instances of anything. No dialog of your own.

To center that on the main window, if you want that, you would pass your window = mainWindow() instance as parent.

P.S.
I see there is also a convenience QApplication.aboutQt() method. So app.aboutQt() should also work.