When using the Fusion style, QMessageBox dialogs show pixelated icons on high DPI monitors.

Simple reproduction using PySide6 version 6.3.1:

from PySide6 import QtGui, QtWidgets


def main():
    app = QtWidgets.QApplication([])
    app.setStyle("Fusion")
    QtWidgets.QMessageBox.question(None, "test", "text")


if __name__ == "__main__":
    main()

Displays the following dialog with Windows display scaling set to 125%:

Without the fusion style, this dialog is displayed (correct):

I think this is a bug because of the following line in the documentation (5.15):

While the macOS style fully supports high-DPI, the Windows desktop style currently has some limitations with certain scale factors. In these cases, consider using the Fusion style instead, which supports high-DPI in all cases.