SIngleton.cs

using UnityEngine;

public class SingletonMonoBehaviour<T> : MonoBehaviour where T : SingletonMonoBehaviour<T> {
    
    static T _inst;

    public static T Instance {
        get {
            if (_inst == null) {
                _inst = GameObject.FindObjectOfType(typeof(T)) as T;
                if (_inst == null) {
                    GameObject singleton = new GameObject();
                    _inst = singleton.AddComponent<T>();
                    _inst.name = $"[{_inst.GetType().Name}]";
                }
            }

            return _inst;
        }
    }
}