Singleton.cs

using UnityEngine;

public abstract class Singleton<T> : MonoBehaviour where T : Component
{
    private static T _instance;

    public static T Instance
    {
        get
        {
            if (_instance == null)
            {
                _instance = FindObjectOfType<T>();

                if (_instance != null) return _instance;
                
                var singletonObject = new GameObject(typeof(T).Name);
                _instance = singletonObject.AddComponent<T>();
                DontDestroyOnLoad(singletonObject);
            }

            return _instance;
        }
    }

    protected virtual void Awake()
    {
        if (_instance == null)
        {
            _instance = this as T;
            DontDestroyOnLoad(this.gameObject);
        }
        else Destroy(this.gameObject);
    }
}