@Aahi You don't have to use this old connection style. Remove SIGNAL and SLOT words.
auto window2 = new MainWindow();
connect(ui->pushButton, &QPushButton::pressed, window2, &MainWindow::some_slot_that_you_have_in_MainWindow_class);
some_slot_that_you_have_in_MainWindow_class()
{
ui->checkBox->setChecked(false);
}
Something like that
