Change the material of unity model as a whole

using System;
using System.Collections.Generic;
using UnityEngine;

public class ModelTransparent : MonoBehaviour
{
    
    /// <summary>
    ///  Used to save the original of the model Material
    /// </summary>
    [HideInInspector] public List<MaterialList> Material_List = new List<MaterialList>();

    /// <summary>
    ///  Transparent material 
    /// </summary>
    public Material MaterialTransparent;

    private void Awake()
    {
    
        RecordOriginalMaterials();
    }

    /// <summary>
    ///  Record the original material of the model 
    /// </summary>
    void RecordOriginalMaterials()
    {
    
        MeshRenderer[] rendererArray = GetComponentsInChildren<MeshRenderer>();
        if (rendererArray.Length != 0)
        {
    
            Material_List.Clear();
            for (int i = 0; i < rendererArray.Length; i++)
            {
    
                int temp = i;
                Material[] materialArray = rendererArray[temp].materials;
                MaterialList materialList = new MaterialList();
                if (materialArray.Length != 0)
                {
    
                    for (int j = 0; j < materialArray.Length; j++)
                    {
    
                        int tempNumber = j;
                        materialList.materialData.Add(materialArray[tempNumber]);
                    }

                    Material_List.Add(materialList);
                }
            }
        }
    }

    /// <summary>
    ///  Model transparency 
    /// </summary>
    public void ChangeModelForTransparent()
    {
    
        MeshRenderer[] rendererArray = GetComponentsInChildren<MeshRenderer>();
        if (rendererArray.Length != 0)
        {
    
            for (int i = 0; i < rendererArray.Length; i++)
            {
    
                int temp = i;
                Material[] ma = rendererArray[temp].materials;
                if (ma.Length != 0)
                {
    
                    for (int j = 0; j < ma.Length; j++)
                    {
    
                        ma[j] = MaterialTransparent;
                    }
                }

                rendererArray[temp].materials = ma;
            }
        }
    }

    /// <summary>
    ///  Restore the original material of the model 
    /// </summary>
    public void ChangeModelMaterialForOriginal()
    {
    
        MeshRenderer[] rendererArray = GetComponentsInChildren<MeshRenderer>();
        if (rendererArray.Length != 0)
        {
    
            for (int i = 0; i < rendererArray.Length; i++)
            {
    
                int temp = i;
                if (i < Material_List.Count)
                {
    
                    rendererArray[temp].materials = Material_List[temp].materialData.ToArray();
                }
            }
        }
    }
}

[Serializable]
public class MaterialList
{
    
    public List<Material> materialData = new List<Material>();

    public MaterialList()
    {
    
    }

    public MaterialList(List<Material> materials)
    {
    
        materialData = materials;
    }
}

Test:

using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class Test : MonoBehaviour
{
    
    private ModelTransparent _modelTransparent;
    public GameObject TestGameObject;
    public List<Button> btns;

    void Start()
    {
    
        _modelTransparent = TestGameObject.GetComponent<ModelTransparent>();
        btns[0].onClick.AddListener(delegate {
     _modelTransparent.ChangeModelForTransparent(); });
        btns[1].onClick.AddListener(delegate {
     _modelTransparent.ChangeModelMaterialForOriginal(); });
    }
}