Is it a good idea and a logic to create adventure game with one scene ?

I mean instead messing with loading scenes and passing variables between the scenes to make one scene and using in the hierarchy empty game objects for each part in the game for example empty game object name main menu and all the childs of it will be main menu objects.

Or instead making a new scene to make one empty gameobject and all it’s childs will be like scenes.

Depends of the game type. But yes, its good to have a big world in a single scene.