App, DontDestroyOnLoad, Keep in Scene changed.

App.cs

using UnityEngine;

public class App : MonoBehaviour
{
    private static App sInstance;

    public static App Instance => sInstance;

    void Awake()
    {
        #region Singleton

        if (sInstance != null)
        {
            Destroy(gameObject);
            return;
        }
        sInstance = this;
        DontDestroyOnLoad(gameObject);

        #endregion
    }
}