How to make round edges for the main window in PyQt?

Question

The question is extremely simple, but I am not succeeding at it at the moment:

What is the simplest way to make round edges to the main window in PyQt/PySide code? I have tried lots of things that can be found online but none works. Here is th simplest example (that is supposed to work in my opinion, but doesn't):

from PySide6.QtWidgets import QApplication, QMainWindow

import sys

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.setStyleSheet("border-radius: 10px;")
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()

    sys.exit(app.exec())

Answer 1

It is not possible to apply the border-radius property of QSS (Qt style Sheets) to QMainWindow.

[evidence1]Qt Style Sheet Reference|Qt Widgets 6.4.2

See the border-radius in List of Properties chapter. border-radius property doesn't support QtMainWindow.

https://doc.qt.io/qt-6/stylesheet-reference.html#brush

This property is supported by QAbstractItemView subclasses, QAbstractSpinBox subclasses, QCheckBox, QComboBox, QFrame, QGroupBox, QLabel, QLineEdit, QMenu, QMenuBar, QPushButton, QRadioButton, QSplitter, QTextEdit, and QToolTip.

[evidence2]Qt Forum|How is it possible to make rounded edges for QMainWindow?

For reference, Qt Forum also posted that border-radius cannot be applied to QSS in the top level window (QMainWindow). https://forum.qt.io/topic/127952/how-is-it-possible-to-make-rounded-edges-for-qmainwindow/2

[Alternative proposal]

If QWidget doesn't lack the functionality you need, you can use it instead of QMainWindow. The following code creates a round QWidget.

from PySide6.QtWidgets import QApplication, QMainWindow
from PySide6.QtWidgets import QWidget
from PySide6.QtCore import Qt

import sys

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        w = 200
        h = 100

        #main window
        self.resize(w, h)
        #remove frame
        self.setWindowFlag(Qt.FramelessWindowHint)
        #make the main window transparent
        self.setAttribute(Qt.WA_TranslucentBackground)

        #round widget
        self.round_widget = QWidget(self)
        self.round_widget.resize(w, h)

        self.round_widget.setStyleSheet(
            """
            background:rgb(255, 255, 255);
            border-radius: 50px;
            """
        )

        #self.setStyleSheet("border-radius: 10px;".format(radius))
        self.show()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = MainWindow()

    sys.exit(app.exec())

The code creates following window.