Steps to reproduce:
1. Open attached project ("focus.zip")
2. Add "scene" scene to build settings
3. Build and run for Windows

4. Run in fullscreen mode("fullscreen.gif" attached):
5. Notice label showing OnApplicationFocus = true
6. Press Win+D
7. Press Win+D again and notice how game isn't brought back up to foreground
8. Notice that if you press Game application on taskbar it is brought back up and shows OnApplicationFocus correctly

Expected behavior in fullscreen mode: Second time you press Win+D the game application is brought back to foreground

9. Run in windowed mode("windowed.gif" attached):
10. Notice label showing OnApplicationFocus = true
11. Press Win+D twice
12. Notice how OnApplicationFocus(true) is not called and game shows that application is not being focused
13. Try to press on Game Application window
14. Notice that OnApplicationFocus isn't called
15. Notice that if you focus another application and then close it, Game application gets focused

Expected behavior in windowed mode: Second time you press Win+D OnApplicationFocus is called returning true

Reproduced with: 5.3.2f1, 5.3.5p5, 5.4.0b22