GameBoy_002_IdentityMaterial.cs

using UnityEngine;

public class Gameboy : MonoBehaviour 
{
  public Material identityMaterial;

  private RenderTexture _downscaledRenderTexture;

  private void OnEnable()
  {
    var camera = GetComponent<Camera>();
    int height = 144;
    int width = Mathf.RoundToInt(camera.aspect * height);
    _downscaledRenderTexture = new RenderTexture(width, height, 16);
    _downscaledRenderTexture.filterMode = FilterMode.Point;
  }

  private void OnDisable()
  {
    Destroy(_downscaledRenderTexture);
  }

  private void OnRenderImage(RenderTexture src, RenderTexture dst)
  {
    Graphics.Blit(src, dst, identityMaterial);
  }
}