Adjust mainwindow size when sub widget is hidden - c++

Question

I'm writing a qt program and trying to resize mainwindow when sub widget is hidden, but there's some difference in Linux and Windows, and I don't know the property way to adjust size in both.
Here's my minimum code:
// MainWindow
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
QWidget *mainWidget = new QWidget(this);
QVBoxLayout *mainlayout = new QVBoxLayout(mainWidget);
QPushButton *hide = new QPushButton(mainWidget);
subwidget *sub = new subwidget(mainWidget);
mainlayout->addWidget(hide);
mainlayout->addWidget(sub);
connect(hide, &QPushButton::clicked, sub, &subwidget::onHide);
setCentralWidget(mainWidget);
adjustSize();
connect(hide, &QPushButton::clicked, this, [&] {
QTimer::singleShot(0, this, [&] { adjustSize(); });
});
}
// Widget
subwidget::subwidget(QWidget *parent)
: QWidget{parent}
{
QVBoxLayout *vlayout = new QVBoxLayout(this);
QPushButton *btn1 = new QPushButton();
btn2 = new QPushButton();
vlayout->addWidget(btn1);
vlayout->addWidget(btn2);
}
void subwidget::onHide()
{
btn2->hide();
}
When I set the timer interval to 1, mainwindow will be the adjusted size when btn2 is hidden in Linux, but it doesn't work in Windows. How can I adjust the mainwindow in windows?
PS: I have tried to add a signal when subwidget is hidden and connect it to adjustSize like connect(sub, &subwidget::hidden, this, [&] { adjustSize(); });, but it also doesn't work.