That is what I assumed. Thanks... Anyway, I have already reinstalled the application from AUR. The same error message during import is there. I thought of doing some 'ln -s' in the python site packages... but even if that solves the issue for me it would be a mess to maintain. I am puzzled about how should I treat each python minor version upgrade. Not only that, but I guessed the Python article on Archwiki should mention some tip, or give any clue...
I hate it when my problems turn to be so obvious that I don't find my way around them.
How shall I proceed?
PS. Also, I see no helpful tips on AUR (en) - syncthing-gtk-python3