After QWebEnginePage (with FullScreenSupportEnabled) sends a signal fullScreenRequested to the customized function self.fullscreen, self.fullscreen can receive the signal and takes a QWebEngineFullScreenRequest instance, but all functions of PySide6 class QWebEngineFullScreenRequest can't work normally, and they will cause a crash of the browser.

You may reproduce the bug through Simple Browser Example with the following code.

# The two lines are added to the end of the function.
def __init__(self):
    ...
    self.webEngineView.settings().setAttribute(QWebEngineSettings.FullScreenSupportEnabled, True)
    self.webEngineView.page().fullScreenRequested.connect(self.fullscreen)

# The following function handles the request for fullscreen.
def fullscreen(self, request):
    request.accept()
    if request.toggleOn() is True:
        self.webEngineView.setWindowFlags(Qt.Window)
        self.webEngineView.showFullScreen()
    else:
        self.webEngineView.setWindowFlags(Qt.Widget)
        self.webEngineView.showNormal()

When self.fullscreen is trying to handle its first line "request.accept()"(I confirmed this by inserting a line like "print('something')" after this line), the browser crashes. It seems that PySide6 class QWebEngineFullScreenRequest can't work normally, so I report it as a bug related to QWebEngineFullScreenRequest.

I tested PySide6's versions 6.2.2.1, 6.2.2, 6.2.1 and 6.2.0. All of them have the bug. I didn't test earlier versions. I tested on Windows and Linux. The bug exists on both of them and there is no any error information when a crash of the program occurs. However, on PyQt6 QWebEngineFullScreenRequest works normally. It seems that the bug is related to PySide6.

Thanks for your reading and attention!