### 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
DisplayServer *ds = memnew(DisplayServerWindows(p_rendering_driver, p_mode, p_vsync_mode, p_flags, p_position, p_resolution, p_screen, r_error));
	if (r_error != OK) {
		if (p_rendering_driver == "vulkan") {
			String executable_name = OS::get_singleton()->get_executable_path().get_file();
			OS::get_singleton()->alert(
					vformat("Your video card drivers seem not to support the required Vulkan version.\n\n"
							"If possible, consider updating your video card drivers or using the OpenGL 3 driver.\n\n"
							"You can enable the OpenGL 3 driver by starting the engine from the\n"
							"command line with the command:\n'%s --rendering-driver opengl3'\n\n"
							"If you have recently updated your video card drivers, try rebooting.",
							executable_name),
					"Unable to initialize Vulkan video driver");
		} else {
			OS::get_singleton()->alert(
					"Your video card drivers seem not to support the required OpenGL 3.3 version.\n\n"
					"If possible, consider updating your video card drivers.\n\n"
					"If you have recently updated your video card drivers, try rebooting.",
					"Unable to initialize OpenGL video driver");
		}
	}
	return ds;
}
void DisplayServerWindows::register_windows_driver() {