Looking for a method to achieve an effect: Place inside post process that does not get affected by it

Image to illustrate: (made with PS)

Im aware that post process essentially is the lens on the camera, but if anyone knows a simple, efficient way to get this effect it would be cool. Doesn’t matter how.

I have looked into:
Try to negate post process effect with a very dim light, didn’t really work
Fog of war, but it looks complicated and can’t find good explanations/tutorials