window display problem

Operating system: win10
Slicer version: 4.11

Expected behavior:
I opened the main window of the slicer in full screen, but when I clicked the button, the pop-up dialog was displayed behind the main window. I thought it was a problem with my own code, I created a small demo, simulated it with the same code, clicked the button and the popup appeared above the main window. So far, my code is fine, but I can’t figure out why.

void qSlicerMainWindowPrivate::init()

q->setFixedSize(QSize(1920, 1080));

//this->StartupState = q->saveState();

Actual behavior:
Click the button, a dialog box will pop up on the main window