Singleton Script

 using UnityEngine;

public abstract class Singleton<T> : MonoBehaviour where T : MonoBehaviour

{

    public static T Instance { get; private set; }

    protected virtual void Awake() => Instance = this as T;

    protected virtual void OnApplicationQuit()

    {

        Instance = null;

        Destroy(gameObject);

    }

}

public abstract class SingletonPersistent<T> : Singleton<T> where T : MonoBehaviour

{

    protected override void Awake()

    {

        if (Instance != null) Destroy(gameObject);

        DontDestroyOnLoad(gameObject);

        base.Awake();

    }

}