I feel this is related to How can I grab a window with widgets and title bar?, but maybe it has a different solution.

When capturing a (window with a) title bar, I get unexpected results after resizing.

from PySide6.QtWidgets import QApplication, QMainWindow, QStyle

application = QApplication()
title_bar_height = application.style().pixelMetric(QStyle.PixelMetric.PM_TitleBarHeight)
window = QMainWindow()
window.show()
screen = window.screen()


def grab_titlebar(width: int) -> None:
    window.resize(width, title_bar_height)
    window.screen().grabWindow(
        window.winId(), x=0, y=-title_bar_height, w=window.width(), h=title_bar_height
    ).save(f"titlebar{width}.png")


grab_titlebar(400)
grab_titlebar(500)
grab_titlebar(300)

400 px:

500 px:

300 px:

How can I make sure the title bar is updated before the snapshot?