PyQt5 window opens then closes in a second

Question

from PyQt5.QtWidgets import QApplication, QPushButton, QMainWindow
from PyQt5.QtGui import QIcon
import sys

class Main(QMainWindow):
    def __init__(self, parent=None) -> None:
        super().__init__(parent=parent)
        self.setWindowTitle("QPushButton")
        left = 300
        top = 200
        width = 300
        height = 250
        self.setGeometry(left, top, width, height)
        self.show()


def main():
    App = QApplication(sys.argv)
    Main()
    sys.exit(App.exec())

if __name__=="__main__":
    main()

I don't get it, it worked before now it closes within a second of opening. I'm thinking somehow my installation got corrupted. Do you have any ideas I tried

def main():
    App = QApplication(sys.argv)
    Main()
    App.exec_()