You had information about the creation of games, who is involved in the development at all https://stepico.com/services/ The game starts with an idea that comes to the mind of the game designer. A framed idea is called a vision. Vision includes the core values of the project and the basic game rules. This is the foundation on which the further design of the game is built, and it cannot be changed at further stages of development, otherwise you will roll back and literally start all over again. Vision can be a text in Google Docs or Notion. There are no universal requirements for its design, it all depends on the studio.