When you take up the design of the game at some point, you find that you need to create a map of links between different game screens.
To create it you need to know what elements the game will consist of. What will be the dependencies between screens and what actions will be done on occasion. This will be the first item that will let you know how complicated it is even a simple game.
It is a picture of the project I work on. Made in DiagramPainter.
Creating such a document allows you to better understand how the game will work. It also reminds you which screens still need to be created.