from PySide6 import QtCore, QtWidgets
import sys

class Window(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.text = QtWidgets.QLabel("Hello World", alignment=QtCore.Qt.AlignCenter)
        self.layout = QtWidgets.QVBoxLayout(self)
        self.layout.addWidget(self.text)

app = QtWidgets.QApplication([])
main_window = Window()
main_window.resize(800, 600)
main_window.show()

sys.exit(app.exec())