A brief tutorial that lists the widget list and gives a couple sample programs.
Lots of great documentation. Cookbook and over 100 sample programs to get you started. Can move back and forth between tkinter and Qt by only changing the import statement. Doesn't require using classes to write your code (unless you want to). Takes 1 line of code to define a widget and place into a window. Qt and Tkinter take 3 to 10 lines per widget.
28 Recipes that you can cut and paste to get an instant example GUI running in a handful of minutes.

The process is:
pip install PySimpleGUI
copy Recipe from Cookbook
Add a GUI onto your command line program in 5 minutes.
Super-simple GUI to grasp... Powerfully customizable.... all on tkinter