from PySide6.QtWidgets import QApplication, QWidget, QMainWindow, QPushButton
import sys

class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()

        self.setWindowTitle('my App')
        button=QPushButton('Press me')

        self.setMinimumSize(400,300)

        self.setCentralWidget(button)

app = QApplication(sys.argv)

window = MainWindow()
window.show()

app.exec()