(UnityEngine) Window for quickly switching between scenes added to your build settings.

SceneSwitcher.cs

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

public class SceneSwitcher : EditorWindow
{
    
    [MenuItem("Tools/SceneSwitcher")]
    public static void ShowWindow()
    {
        GetWindow<SceneSwitcher>().minSize = new Vector2(100, 25);
    }

    [SerializeField] private static Scene activeScene;

    void OnSceneSelected(object scene)
    {
        EditorSceneManager.SaveOpenScenes();
        activeScene = EditorSceneManager.OpenScene(((string) scene));
    }
    
    private void OnGUI()
    {
        activeScene = EditorSceneManager.GetActiveScene();

        if (GUILayout.Button("Select Scene"))
        {
            // create the menu and add items to it
            GenericMenu menu = new GenericMenu();
            
            for (int i = 0; i < SceneManager.sceneCountInBuildSettings; i++)
            {
                String scenePath = SceneUtility.GetScenePathByBuildIndex(i);
                String sceneName = scenePath.Substring(0, scenePath.Length - 6).Substring(scenePath.LastIndexOf('/') + 1);
                menu.AddItem(new GUIContent(sceneName), scenePath.Equals(activeScene.path), OnSceneSelected, scenePath);
            }
            // display the menu
            menu.ShowAsContext();
        }
    }
}