FocusOnPlayDummyWindow

using UnityEditor;

[InitializeOnLoad]
public class FocusOnPlayDummyWindow : EditorWindow {
    static FocusOnPlayDummyWindow _instance;
    static bool IsOpen { get { return _instance != null; } }

    [MenuItem("Window/Focus on Play Dummy Window")]
    static FocusOnPlayDummyWindow GetFocusOnPlayDummyWindow() {
        FocusOnPlayDummyWindow window = GetWindow<FocusOnPlayDummyWindow>("Dummy");

        window.Show();

        return window;
    }

    void OnEnable() {
        _instance = this;
    }

    void OnDisable() {
        _instance = null;
    }

    static FocusOnPlayDummyWindow() {
        EditorApplication.playModeStateChanged += OnPlayModeChanged;
    }

    static void OnPlayModeChanged(PlayModeStateChange playModeStateChange) {
        if (!IsOpen) { return; }

        switch (playModeStateChange) {
            case PlayModeStateChange.ExitingEditMode:
                GetFocusOnPlayDummyWindow().Focus();
                break;
            case PlayModeStateChange.EnteredEditMode:
                GetWindow<SceneView>().Focus();
                break;
        }
    }
}