ThermalController.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.Rendering.PostProcessing;

public class ThermalController : MonoBehaviour
{
    public Shader ThermalShader;
    float IntensityThermal;
    bool thermal;
    [SerializeField]
    PostProcessVolume postProcessVolume;
    Camera cam;
    // Start is called before the first frame update
    void Start()
    {
        cam = GetComponent<Camera>();
        cam.enabled = false;
    }

    // Update is called once per frame
    void Update()
    {
        if (Input.GetKeyDown(KeyCode.T))
        {
            thermal = !thermal;
            SwitchThermal(thermal);
        }
    }

    void SwitchThermal(bool thermalB)
    {
        if (thermalB)
        {
            cam.enabled = true;
            IntensityThermal = 1;
            if(postProcessVolume != null)
            {
                postProcessVolume.weight = IntensityThermal;
            }
            cam.SetReplacementShader(ThermalShader, "ThermalVision");

        }
        else
        {
            cam.enabled = false;
            IntensityThermal = 0;
            if (postProcessVolume != null)
            {
                postProcessVolume.weight = IntensityThermal;
            }
            cam.ResetReplacementShader();
        }
    }
}