Basic PyQt5 application to run in ArcGIS Pro custom script tool: running in own thread

arcgispro_basic_app_threading.py

import sys
import threading
import arcpy
from PyQt5.QtWidgets import (QMainWindow, QLabel, QApplication)
from PyQt5.QtCore import Qt


class MainWindow(QMainWindow):
    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.setWindowTitle("Basic App")

        product = arcpy.CheckProduct('arcview')
        label = QLabel(
            "Q: Is `arcview` license available? \n A: {}".format(product))
        label.setAlignment(Qt.AlignCenter)
        self.setCentralWidget(label)


def main():
    app = QApplication(sys.argv)
    ex = MainWindow()
    ex.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    t = threading.Thread(target=main)
    t.start()