Unity Editor script to toggle loading entry scene at beginning of play mode.

PlayModeEntryMenu.cs

/// <summary>
/// Menu options to enable or disable the loading of the 0th index entry scene in the build settings when play mode
/// is started. This is useful if you are working on a scene that is later in the intended scene flow of your game when
/// developing. 
/// </summary>
[InitializeOnLoad]
public static class PlayModeEntryMenu
{
    private const string EntryLoadKey = "editor.entry.load";
    private static string _prevScene;

    static PlayModeEntryMenu()
    {
        if (!PlayerPrefs.HasKey(EntryLoadKey)) PlayerPrefs.SetInt(EntryLoadKey, 0);
        EditorApplication.playModeStateChanged += change =>
        {
            if (change != PlayModeStateChange.ExitingEditMode) return;
            if (PlayerPrefs.GetInt(EntryLoadKey) != 1) return;
            var firstScene = EditorBuildSettings.scenes[0].path;
            var entryAsset = AssetDatabase.LoadAssetAtPath<SceneAsset>(firstScene);
            EditorSceneManager.playModeStartScene = entryAsset;
        };
    }

    [MenuItem("File/Play Mode/Enable Entry Load")]
    public static void EnableEntryLoad()
    {
        PlayerPrefs.SetInt(EntryLoadKey, 1);
    } 

    [MenuItem("File/Play Mode/Enable Entry Load", true)]
    public static bool EnableEntryLoadValidate()
    {
        return PlayerPrefs.GetInt(EntryLoadKey) == 0;
    } 

    [MenuItem("File/Play Mode/Disable Entry Load")]
    public static void DisableEntryLoad()
    {
        PlayerPrefs.SetInt(EntryLoadKey, 0);
    } 

    [MenuItem("File/Play Mode/Disable Entry Load", true)]
    public static bool DisableEntryLoadValidate()
    {
        return PlayerPrefs.GetInt(EntryLoadKey) == 1;
    } 
}

I created this Unity Editor script to help with simply starting Play Mode with the game's entry scene without having to go between the entry scene and the scene I am actively working on.