Singleton for Unity. Could possibly be improved on.

Singleton.cs

using UnityEngine;
using UnityEngine.Assertions;

public class Singleton<T> : BaseBehaviour where T : MonoBehaviour
{
    public static T Instance => GetInstance();

    /// <summary>GetInstance gets called by the getter Instance, however GetInstance can be used to get extra control such as turning off exceptions and allowing null or generate the instance when it can't be found </summary>
    public static T GetInstance(bool throwException = true, bool generateInstance = false)
    {
        if (instance == null)
        {
            T[] foundInstances = FindObjectsOfType<T>(true);
            if (foundInstances.Length == 0)
            {
                if (generateInstance)
                {
                    GameObject gameObject = new GameObject($"{typeof(T).Name} Manager");
                    instance = gameObject.AddComponent<T>();
                }
            }
            else
            {
                if (foundInstances.Length > 1)
                    Debug.LogError($"You have multiple instances of a Singleton of type {typeof(T).Name}");
                instance = foundInstances[0];
            }

            if (throwException)
                Assert.IsTrue(instance, $"The component {typeof(T).FullName}, could not be found in the scene");
        }

        return instance;
    }

    private static T instance;
}