JJBB/Assets/Project/Script/Player/Controller/CameraGrayEffect.cs

using UnityEngine;
public class CameraGrayEffect : MonoBehaviour
{
    public Material mat;
    private void OnRenderImage(RenderTexture src, RenderTexture dest)
    {
        if (mat == null)
            return;
        Graphics.Blit(src, dest, mat);
    }
}