Singleton for Unity

using UnityEngine;

public class Managers : MonoBehaviour
{
    private static Managers Instance;

    public static Managers GetInstance() { return Instance; }

    void Start()
    {
        GameObject go = GameObject.Find("@Managers");
        Instance = go.GetComponent<Managers>();
    }

    void Update() { }
}

using UnityEngine;

public class Managers : MonoBehaviour
{
    private static Managers s_Instance;

    // 1.
    // Use the Instance property to access s_Instance
    public static Managers Instance
    {
        get
        {
            Init();
            return s_Instance;
        }
    }

    static void Init()
    {
        // 2.
        // Called through the Instance property

        if (s_Instance == null)
        {
            // 2-1.
            // If s_Instance is null (which it will be the first time),
            // try to find a GameObject named "@Managers"
            GameObject go = GameObject.Find("@Managers");

            // 3.
            // If no such GameObject exists (i.e., not found in the Hierarchy)
            if (go == null)
            {
                // 4.
                // Create a new GameObject named "@Managers"
                // and add the Managers component to it
                go = new GameObject() { name = "@Managers" };
                go.AddComponent<Managers>();
            }

            // 3-1.
            // If the GameObject "@Managers" already exists,
            // make sure it is not destroyed on scene changes
            // and assign the Managers component to s_Instance
            DontDestroyOnLoad(go);
            s_Instance = go.GetComponent<Managers>();
        }
    }
}