### 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
CloseHandle(power_request);
		power_request = nullptr;
	}
	keep_screen_on = p_enable;
}
bool DisplayServerWindows::screen_is_kept_on() const {
	return keep_screen_on;
}
Vector<DisplayServer::WindowID> DisplayServerWindows::get_window_list() const {
	_THREAD_SAFE_METHOD_
	Vector<DisplayServer::WindowID> ret;
	for (const KeyValue<WindowID, WindowData> &E : windows) {
		ret.push_back(E.key);
	}
	return ret;
}
DisplayServer::WindowID DisplayServerWindows::get_window_at_screen_position(const Point2i &p_position) const {
	Point2i offset = _get_screens_origin();
	POINT p;
	p.x = p_position.x + offset.x;
	p.y = p_position.y + offset.y;
	HWND hwnd = WindowFromPoint(p);
	for (const KeyValue<WindowID, WindowData> &E : windows) {
		if (E.value.hWnd == hwnd) {
			return E.key;
		}
	}
	return INVALID_WINDOW_ID;
}
DisplayServer::WindowID DisplayServerWindows::create_sub_window(WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Rect2i &p_rect) {