if __name__ == '__main__':
    import sys
    app = QtWidgets.QApplication(sys.argv)
    mainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()  # 这个是类名，名字根据自定义的情况变化
    ui.setupUi(mainWindow)
    mainWindow.show()
    sys.exit(app.exec())

from PyQt6.QtWidgets import QMessageBox

self.pushButton.clicked.connect(self.btnClick)

    def btnClick(self):
        val = QMessageBox.question(self.mainWindow, "提示框", "欢迎进入PyQt5编程世界",QMessageBox.StandardButton.Yes|QMessageBox.StandardButton.No)