How to make an area around the player be affected by a post process (with a 3rd person point of view)

Development Rendering
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You make a post process material that is black and white. You then apply it to the post process material which is placed in said area. Here is a tutorial for it: How To Add Post Process Material | Community tutorial

It’s very simple to add and you should be able to do it very easily. For the shader you want to get the scene texture node and the PostProcessInput0 to modify.