I have a python snap which I am trying to move from core18 to core20 /22. When changing base to core22 and building the snap. The snap is not able to find the installed python packages in $SNAP/lib/python3.10/site-packages. The hack is to set PYTHONPATH environment variable explicitly under environment section.
I don’t think this is causing your problem, but this environment variable should be PARTS_PYTHON_INTERPRETER in core22. I’ll update the migration howto accordingly (@rpjday might be interested in this change).
The reason is that plugins are now implemented in a library shared by different *craft tools, so they can’t use Snapcraft-specific variable names.