### Godot version

4.0.beta12

### System information

Windows 11, RTX 3080

### Issue description

When a Window Node is created with it's Transparent flag set to true and Project Settings --> Display --> Window --> Subwindows --> Embed Subwindows is false, the Window has a black background. By cycling the transparent flag from false and back to true again, during runtime, the window's background then becomes transparent. 

### Steps to reproduce

Attempt to create a Non-embedded Subwindow with a transparent background using the appropriate flags. 

### Minimal reproduction project

Note: this project is from Reddit user [gongpha](https://www.reddit.com/user/gongpha/) and his Reddit post [Learning a Godot 4.0 Window node](https://www.reddit.com/r/godot/comments/xr8yxn/learning_a_godot_40_window_node/)

https://github.com/gongpha/godot4-window-test
}
#endif
			}
			if (!window.minimized && (!(window_pos_params->flags & SWP_NOMOVE) || window_pos_params->flags & SWP_FRAMECHANGED)) {
				window.last_pos = window_client_rect.position;
				rect_changed = true;
			}
			if (rect_changed) {
				if (!window.rect_changed_callback.is_null()) {
					Variant size = Rect2i(window.last_pos.x, window.last_pos.y, window.width, window.height);
					const Variant *args[] = { &size };
					Variant ret;
					Callable::CallError ce;
					window.rect_changed_callback.callp(args, 1, ret, ce);
				}
			}
			
			
			return 0;
		} break;
		case WM_ENTERSIZEMOVE: {
			Input::get_singleton()->release_pressed_events();
			windows[window_id].move_timer_id = SetTimer(windows[window_id].hWnd, 1, USER_TIMER_MINIMUM, (TIMERPROC) nullptr);
		} break;
		case WM_EXITSIZEMOVE: {
			KillTimer(windows[window_id].hWnd, windows[window_id].move_timer_id);
		} break;
		case WM_TIMER: {
			if (wParam == windows[window_id].move_timer_id) {
				_process_key_events();