Problems loading python plugins into qt designer

[Zbigniew Reszela]

Dear all,

I have experienced problems loading python plugins into the Qt Designer.

I follow this guide on developing custom python plugins: 
https://www.riverbankcomputing.com/static/Docs/PyQt5/designer.html#writing-qt-designer-plugins.

I can not even load the example plugins that comes with the PyQt5 source 
package.

I use the latest PyQt5 and Qt5 packages available on conda-forge:

OS: Debian 11

python (conda) = 3.11.5

Qt5 = 5.15.8

PyQt5 = 5.15.9

I execute it in the following way:

╰─>$ PYTHONPATH=/PyQt5-5.15.9/examples/designer/plugins/widgets 
PYQTDESIGNERPATH=/PyQt5-5.15.9/examples/designer/plugins/python/ designer

Do you know what could be wrong?

Do you know how could I debug this problem?

I don't see that the plugins are even attempted to be loaded, no 
__pycache__ dir is generated with pyc files.

I was thinking on adding some prints in the 
/PyQt5-5.15.9/designer/pluginloader.cpp, compiling and somehow linking 
it with the designer. Any hint on that?

Note, when I use some older versions of PyQt5 and Qt5 from some older 
conda environment I prepared in the past it works correctly and I can 
see the plugins loaded in the designer, the same using the Debian 11 
packages:

OS: Debian 11

python (conda) = 3.9.2

Qt5 = 5.12.9

PyQt5 = 5.12.3

Here I can see __pycache__ dir with pyc files.

Many thanks in advance for any kind of help,

Regards,

Zibi