In the scene view, there's a control bar with a 'lighting' button that lets you toggle scene view lighting. This turns off all shadows and all light sources, i.e. makes it so that all objects are seen as fully bright on all sides. How do I do the same for the game view?
The scene lightning button doesn't just disable scene lights, it activates another lighting mode or adds hidden lights to the scene.
If you would just turn of all lights, all objects would apear black.
I don't know how exactly the scene is illuminated while the lights are off in the scene view.
According to this (very old) post, the scene lighting is done with a directional light that is parented to the camera.
It's about 0.75 itensity and of gray color.
It looks the same way as the camera.
The scene lighting might have changed, as that post is from 2008.
Another way how to do it:
Blender does something similar.
It adds 4 lights to the scene and attaches them to the scene camera.
This adds some more smoothing to the light while still giving a sense of shading and direction.