PySide2 Error: This application failed to start because no Qt platform plugin could be initialized
Add at the first:

import sys,os
import PySide2
 
dirname = os.path.dirname(PySide2.__file__)
plugin_path = os.path.join(dirname, 'plugins', 'platforms')
os.environ['QT_QPA_PLATFORM_PLUGIN_PATH'] = plugin_path