A free extract from the official core book of the RPG:
The Domestic is an introductory scenario designed for one player, based on Ben Aaronovitch’s short story of the same name. Choose to play as a magic-wielding police officer, nurse, or social worker in a game set in the world of Ben Aaronovitch’s hugely successful Rivers of London series.
Armed with this book, a pencil, and some roleplaying dice, you are ready to take on your first case for the Folly. No GM needed!
It is one approach, and goes back to a long time ago with choose your own adventure books.
There are other, less on rails approaches, where you play an RPG and replace what usually would be GM decisions by random tables (concrete and inspirational) and mechanics that introduce complications and challenges.
That's exactly what came to mind.