1- Create new project.
2- Create new object and make a new sprite in piskle (just a box or anything), the point in this step is to just make something to show in the resources page.
3- Go to resources page
4- Scan .json file
5- game.json will show up
6- Remove unused .json
7- it will remove game.json
game.json is being used, how GDevelop is reading it as unused ? while its actually the project it self 
No, it’s not. This is the resources screen. The game.json is a project file, it contains events, settings, etc. It is not used in the end game. A resource is an asset that needs to be exported with the game to be used within it. Since the game.json is not being used as a resource, meaning in your events or objects, anywhere in your game, this resource is indeed unused. The fact that it isn’t there by default and you need to add it as a resource before it shows up should tell you that game.json isn’t and isn’t meant to be a resource.