Earlier quoted context omitted.
If you use the complete Qt installer, you get QtDesigner. If you use the PyQT-provided wheels and/or you don'want to mess with the whole Qt, then you can separately install QtCreator, which is very simple and embeds QtDesigner.
Looking at a tutorial, it looks like all it does is layout the form for you. That's a shame. Things closer to what the original VB was are sorely missed in modern computing.
Also - layouts in VB/Delphi weren't responsive, layouts made in QtDesigner are.