### 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
} else {
				
				wd.layered_window = false;
				DWM_BLURBEHIND bb;
				ZeroMemory(&bb, sizeof(bb));
				HRGN hRgn = CreateRectRgn(0, 0, -1, -1);
				bb.dwFlags = DWM_BB_ENABLE | DWM_BB_BLURREGION;
				bb.hRgnBlur = hRgn;
				bb.fEnable = FALSE;
				DwmEnableBlurBehindWindow(wd.hWnd, &bb);
			}
		} break;
		case WINDOW_FLAG_NO_FOCUS: {
			wd.no_focus = p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_MOUSE_PASSTHROUGH: {
			wd.mpass = p_enabled;
			_update_window_mouse_passthrough(p_window);
		} break;
		case WINDOW_FLAG_POPUP: {
			ERR_FAIL_COND_MSG(p_window == MAIN_WINDOW_ID, "Main window can't be popup.");
			ERR_FAIL_COND_MSG(IsWindowVisible(wd.hWnd) && (wd.is_popup != p_enabled), "Popup flag can't changed while window is opened.");
			wd.is_popup = p_enabled;
		} break;
		default:
			break;
	}
}
bool DisplayServerWindows::window_get_flag(WindowFlags p_flag, WindowID p_window) const {