Scene Hierarchy Window is a Unity window that simplifies and speeds up the management of scenes that are loaded/unloaded/active in the hierarchy

SceneHierarchyWindow.cs

// Created using Unity 2023.2, but if I'm not mistaken, this should work in older versions of Unity too

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

namespace Whitakr.Utils.Editor
{
	public class SceneHierarchyWindow : EditorWindow
	{
		const float LABEL_PADDING = 10f;
		const float BUTTON_WIDTH = 80f;
		
		[MenuItem("Whitakr/Utils/Scene Hierarchy Window")]
		public static void ShowWindow()
		{
			SceneHierarchyWindow window = GetWindow<SceneHierarchyWindow>();
			window.titleContent = new("Scene Hierarchy Window");
			window.Show();
		}
		
		void OnGUI()
		{
			if (Application.isPlaying)
			{
				EditorGUILayout.HelpBox("Scene Hierarchy Window is not available in Play Mode.", MessageType.Info);
				return;
			}
			
			SceneSetup[] setups = EditorSceneManager.GetSceneManagerSetup();

			float previousLabelWidth = EditorGUIUtility.labelWidth;
			float minLabelWidth = setups
				.Select(setup => System.IO.Path.GetFileNameWithoutExtension(setup.path))
				.Select(sceneName => GUI.skin.label.CalcSize(new(sceneName)).x)
				.Max();
			
			EditorGUIUtility.labelWidth = minLabelWidth + LABEL_PADDING;
			foreach (SceneSetup setup in setups)
			{
				string scenePath = setup.path;
				string sceneName = System.IO.Path.GetFileNameWithoutExtension(scenePath);
				EditorGUILayout.BeginHorizontal();
				EditorGUILayout.PrefixLabel(sceneName);
				
				if (setup.isActive)
				{
					EditorGUILayout.LabelField("Active", EditorStyles.boldLabel);
				}
				else
				{
					if (setup.isLoaded)
					{
						if (GUILayout.Button("Unload", GUILayout.Width(BUTTON_WIDTH)))
						{
							Unload(scenePath);
						}
					}
					else
					{
						if (GUILayout.Button("Load", GUILayout.Width(BUTTON_WIDTH)))
						{
							Load(scenePath);
						}
					}
					
					if (GUILayout.Button("Set Active", GUILayout.Width(BUTTON_WIDTH)))
					{
						SetActive(scenePath);
					}
				}

				EditorGUILayout.EndHorizontal();
			}

			if (setups.Any(s => !s.isLoaded))
			{
				if (GUILayout.Button("Load All"))
				{
					foreach (SceneSetup setup in setups)
					{
						if (!setup.isLoaded)
						{
							Load(setup.path);
						}
					}
				}
			}
			else if (setups.Length > 1) // Only show unload all if there are multiple scenes loaded, since Active scene can't be unloaded
			{
				if (GUILayout.Button("Unload All"))
				{
					foreach (SceneSetup setup in setups)
					{
						if (setup.isLoaded && !setup.isActive)
						{
							Unload(setup.path);
						}
					}
				}
			}
			
			EditorGUIUtility.labelWidth = previousLabelWidth;
		}

		static void Load(string scenePath)
		{
			EditorSceneManager.OpenScene(scenePath, OpenSceneMode.Additive);
		}

		static void Unload(string scenePath)
		{
			EditorSceneManager.CloseScene(SceneManager.GetSceneByPath(scenePath), false);
		}
		
		static void SetActive(string scenePath)
		{
			Scene scene = SceneManager.GetSceneByPath(scenePath);
			if (!scene.isLoaded)
			{
				EditorSceneManager.OpenScene(scenePath, OpenSceneMode.Additive);
			}

			SceneManager.SetActiveScene(scene);
		}
	}
}