I encountered this error while I was using PySIde2 and Custom-Widgets to build a school project when following this tutorial on YouTube. After installing the Custom Widgets using pip and creating a new project space using Python I got the following error while trying to start the app.

After some days of searching Stackoverflow and looking for working solutions online, I couldn't get it to work, so I decided to debug the error by reviewing the source code of the files created by the Custom_Widgets module It turned out in one of the file called QSS_Resources_rc.py a module called QtCore was imported from PyQt5 instead of PySIde2 this where contradictions would occur since from our main file PySIde2 was the main module and the implementation is a bit different from PyQt5 which would make it to not to see the package path "/lib/python3.11/site-packages/PySide2/Qt/lib/libQt5Core.so.5" and use this path "/lib/python3.11/site-packages/PyQt/Qt/lib/libQt5Core.so.5".

Solving the error is as simple as changing this statement in the QSS_Resources_rc.py file

from PyQt5 import QtCore to from PySide2 import QtCore

We rerun the app and everything was good