### 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
if (is_dark_mode_supported() && dark_title_available) {
				BOOL value = is_dark_mode();
				::DwmSetWindowAttribute(windows[window_id].hWnd, DWMWA_USE_IMMERSIVE_DARK_MODE, &value, sizeof(value));
			}
		} break;
		case WM_SYSCOMMAND: 
		{
			switch (wParam) 
			{
				case SC_SCREENSAVE: 
				case SC_MONITORPOWER: 
					return 0; 
				case SC_KEYMENU:
					if ((lParam >> 16) <= 0) {
						return 0;
					}
			}
		} break;
		case WM_CLOSE: 
		{
			if (windows[window_id].focus_timer_id != 0U) {
				KillTimer(windows[window_id].hWnd, windows[window_id].focus_timer_id);
			}
			_send_window_event(windows[window_id], WINDOW_EVENT_CLOSE_REQUEST);
			return 0; 
		}
		case WM_MOUSELEAVE: {
			if (window_mouseover_id == window_id) {
				old_invalid = true;
				window_mouseover_id = INVALID_WINDOW_ID;