SceneUtils, GetAllRootGameObjects, DontDestroyOnLoadScene, etc.

SceneExtensions.cs

using System.Linq;
using UnityEngine;
using UnityEngine.SceneManagement;

public static class SceneExtensions
{
    /// <summary>
    /// Returns whether the given scene contains the given component on any of its GameObjects.
    /// </summary>
    public static bool HasComponent<T>(this Scene scene)
    {
        return scene.GetRootGameObjects().Any(rootGameObject => rootGameObject.GetComponentsInChildren<T>().Any());
    }
}

SceneUtils.cs

using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using UnityEngine.SceneManagement;

public static class SceneUtils
{
    private static Scene? _dontDestroyOnLoadScene = null;
    public static Scene DontDestroyOnLoadScene
    {
        get
        {
            _dontDestroyOnLoadScene ??= GetDontDestroyOnLoadScene();
            return _dontDestroyOnLoadScene.Value;
        }
    }

    /// <summary>
    /// Returns the Scene that objects go in when we call <see cref="Object.DontDestroyOnLoad"/> on them.
    /// </summary>
    /// <remarks>
    /// Hacky because Unity... See:<br/>
    /// https://forum.unity.com/threads/editor-script-how-to-access-objects-under-dontdestroyonload-while-in-play-mode.442014/#post-3570916<br/>
    /// https://github.com/yasirkula/UnityRuntimeInspector/blob/12bd2d85fd5e571756d2783338d9a17706e87263/Plugins/RuntimeInspector/Scripts/RuntimeHierarchy.cs#L1523
    /// </remarks>
    private static Scene GetDontDestroyOnLoadScene()
    {
        GameObject temp = null;
        try
        {
            temp = new GameObject();
            Object.DontDestroyOnLoad(temp);
            var dontDestroyOnLoadScene = temp.scene;
            Object.DestroyImmediate(temp);
            temp = null;

            return dontDestroyOnLoadScene;
        }
        catch (System.Exception e)
        {
            Debug.LogException(e);
            return new Scene();
        }
        finally
        {
            if (temp != null)
            {
                Object.DestroyImmediate(temp);
            }
        }
    }

    public static IEnumerable<Scene> GetAllLoadedScenes(bool includeDontDestroyOnLoadScene = true)
    {
        for (var i = 0; i < SceneManager.sceneCount; i++)
        {
            yield return SceneManager.GetSceneAt(i);
        }

        if (includeDontDestroyOnLoadScene)
        {
            yield return DontDestroyOnLoadScene;
        }
    }

    public static IEnumerable<GameObject> GetAllRootGameObjects(bool includeDontDestroyOnLoadScene = true)
    {
        static GameObject[] GetRootGameObjects(Scene scene) => scene.GetRootGameObjects();
        return GetAllLoadedScenes(includeDontDestroyOnLoadScene).SelectMany(GetRootGameObjects);
    }

    public static bool HasComponentInAnyLoadedScene<T>(bool includeDontDestroyOnLoadScene = true)
    {
        return GetAllLoadedScenes(includeDontDestroyOnLoadScene).Any(SceneExtensions.HasComponent<T>);
    }
}