### 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
_THREAD_SAFE_METHOD_
	ERR_FAIL_COND(!windows.has(p_window));
	WindowData &wd = windows[p_window];
	switch (p_flag) {
		case WINDOW_FLAG_RESIZE_DISABLED: {
			wd.resizable = !p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_BORDERLESS: {
			wd.borderless = p_enabled;
			_update_window_style(p_window);
			_update_window_mouse_passthrough(p_window);
			ShowWindow(wd.hWnd, (wd.no_focus || wd.is_popup) ? SW_SHOWNOACTIVATE : SW_SHOW); 
		} break;
		case WINDOW_FLAG_ALWAYS_ON_TOP: {
			ERR_FAIL_COND_MSG(wd.transient_parent != INVALID_WINDOW_ID && p_enabled, "Transient windows can't become on top");
			wd.always_on_top = p_enabled;
			_update_window_style(p_window);
		} break;
		case WINDOW_FLAG_TRANSPARENT: {
			if (p_enabled) {
				
				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 = TRUE;
				DwmEnableBlurBehindWindow(wd.hWnd, &bb);
				wd.layered_window = true;