You're free to create stories, video, of your own video game in the universe. If you chose to make that public domain and give it away for free, then good on you.
Others can create freely in this universe with their own expression, which they could charge for.
Much like how there are movies about Cinderella or Red Riding Hood which are under copyright, but the base story itself is in the public domain and free to use.
I recommend the Overdrive app. sign up (in the app, even!) for a library card (doesn't necessarily need to be to your local library) and start checking the books out!
Always worth checking if there's more libraries you're eligible for, for the best selection - I've got a card through my local library, one from the next town over (I just need to visit once a year to renew), and a town in California (Sunnyvale) that gives library accounts to anyone who applies. Some libraries will do digital-only accounts for like $20/Year, so that could be worth looking into if your local library doesn't support Overdrive/Libby.
As of now, 15 September 2023, the comic book property called Fables, including all related Fables spin-offs and characters, is now in the public domain. What was once wholly owned by Bill Willingham is now owned by everyone, for all time.
The author has relinquished his copyright on the Fables universe. Every work based on it has its own copyright, however.
So while you can make your own stories in the Fables universe, it doesn't mean that things like The Wolf Among Us game from Telltale have had their copyrights affected in any way.