The issue happens in an Anaconda environment with the Qt conda-forge package installed (or previously installed).

After having installed the latest wheel on PyPi (5.11.1), the application fails to start with the error message:

"This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem."

If I run the app after having set QT_DEBUG_PLUGINS=1, I get:

QFactoryLoader::QFactoryLoader() checking directory path "C:/Users/xxxxx/AppData/Local/py3/platforms" ...
qt.qpa.plugin: Could not find the Qt platform plugin "windows" in ""

Such a folder does not exist. If I add the right path to the code (using QCoreApplication.addLibraryPath), it works.

The issue is related to a custom `qt.conf` being copied aside the Python interpreter (and not removed in case of uninstallation of the Qt conda package).

Uninstall the Qt conda package and manually remove the relic `qt.conf` solves the issue.