非同步載入場景分為A、B、C三個場景

A場景是開始場景；B場景是載入場景（進度條載入顯示）；C場景是目標場景

在A場景中新增一個按鈕，觸發函式：

//非同步載入新場景  
public void LoadNewScene()  
{  
    //儲存需要載入的目標場景  
    Globe.nextSceneName = "Scene";  
  
    SceneManager.LoadScene("Loading");        
}  

在B場景中新增一個指令碼(AsyncLoadScene)，掛載到Camera下

using System.Collections;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;

public class Globe
{
    public static string nextSceneName;

    /// <summary>
    /// 非同步載入場景
    /// </summary>
    /// <param name="sceneName">場景名字</param>
    /// <param name="isAsync">是否使用非同步載入</param>
    public static void LodingScene(string sceneName, bool isAsync = true)
    {
        //清理Unity垃圾
        Resources.UnloadUnusedAssets();
        //清理GC垃圾
        System.GC.Collect();
        //是否使用非同步載入
        if (isAsync)
        {
            //賦值載入場景名稱
            nextSceneName = sceneName;
            //跳轉到LoadingScene場景
            SceneManager.LoadScene("LoadingScene");
        }
        else
        {
            SceneManager.LoadScene(sceneName);
        }
    }
    
}
/// <summary>
/// 非同步載入指令碼
/// </summary>
public class AsyncLoadScene : MonoBehaviour
{
    public Slider loadingSlider;

    //public Text Tips;
    //public Text loadingText;

    //private float loadingSpeed = 1;

    //private float targetValue;

    private AsyncOperation operation;

    private int displayProgress;
    private int toProgress;

    void Start()
    {
        loadingSlider.value = 0;
        loadingSlider.maxValue = 100;

        if (SceneManager.GetActiveScene().name == "LoadingScene")
        {
            //啟動協程  
            StartCoroutine(AsyncLoading());
        }
    }
    private IEnumerator AsyncLoading()
    {
        operation = SceneManager.LoadSceneAsync(Globe.nextSceneName);
        operation.allowSceneActivation = false;
        while (operation.progress < 0.9f)
        {
            toProgress = (int)operation.progress * 100;
            while (displayProgress < toProgress)
            {
                ++displayProgress;
                SetLoadingPercentage(displayProgress);
                yield return new WaitForEndOfFrame();
            }
        }
        toProgress = 100;
        while (displayProgress < toProgress)
        {
            ++displayProgress;
            SetLoadingPercentage(displayProgress);
            yield return new WaitForEndOfFrame();
        }
        operation.allowSceneActivation = true;
    }

    private void SetLoadingPercentage(int Percentage)
    {
        loadingSlider.value = Percentage;
        //loadingText.text = Percentage + "%";
    }

  
}

這裡需要注意的是使用AsyncOperation.allowSceneActivation屬性來對非同步載入的場景進行控制

為true時，非同步載入完畢後將自動切換到C場景

最後附上效果圖