It seems like, even if you decide your FOSS use falls under hobbyist (and it's not clear if that's necessarily valid), if anyone wants to pull your project and run it, they'll need to set up their own simplegui account and get a key etc...
>" 7. If I ship a product that uses PySimpleGUI do I have to pay royalties to PySimpleGUI? No. To ship a product, commercial users embed Distribution Keys (at no cost) into each application shipped.
Hobbyist Users may share their projects. Each recipient will be able to run the project during a trial period. After the trial period, the recipient must subscribe to PySimpleGUI (at no cost) to obtain their own Developer Key. " from: https://pysimplegui.com/faq