### 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
return tablet_drivers.size();
}
String DisplayServerWindows::tablet_get_driver_name(int p_driver) const {
	if (p_driver < 0 || p_driver >= tablet_drivers.size()) {
		return "";
	} else {
		return tablet_drivers[p_driver];
	}
}
String DisplayServerWindows::tablet_get_current_driver() const {
	return tablet_driver;
}
void DisplayServerWindows::tablet_set_current_driver(const String &p_driver) {
	if (tablet_get_driver_count() == 0) {
		return;
	}
	bool found = false;
	for (int i = 0; i < tablet_get_driver_count(); i++) {
		if (p_driver == tablet_get_driver_name(i)) {
			found = true;
		}
	}
	if (found) {
		_update_tablet_ctx(tablet_driver, p_driver);
		tablet_driver = p_driver;
	} else {
		ERR_PRINT("Unknown tablet driver " + p_driver + ".");
	}
}
DisplayServerWindows::DisplayServerWindows(const String &p_rendering_driver, WindowMode p_mode, VSyncMode p_vsync_mode, uint32_t p_flags, const Vector2i *p_position, const Vector2i &p_resolution, int p_screen, Error &r_error) {