Nevertheless it's just such a delightful gulp of fresh air to open the repo of a GUI app and see it's not in JavaScript :-) An Electron instance with the same would probably take even more memory, wouldn't it?
Also I didn't find a way to install Qt on Windows without later receiving E-Mails from Trolltech (or The Qt Company, nowadays) trying to sell Qt to me.
pip install pyqt5-tools gets you everything incl the designer :-)
It may fail building though.