### 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_
	if (!windows.has(last_focused_window)) {
		return; 
	}
	
	
	String text = p_text.replace("\r\n", "\n").replace("\n", "\r\n"); 
	if (!OpenClipboard(windows[last_focused_window].hWnd)) {
		ERR_FAIL_MSG("Unable to open clipboard.");
	}
	EmptyClipboard();
	Char16String utf16 = text.utf16();
	HGLOBAL mem = GlobalAlloc(GMEM_MOVEABLE, (utf16.length() + 1) * sizeof(WCHAR));
	ERR_FAIL_COND_MSG(mem == nullptr, "Unable to allocate memory for clipboard contents.");
	LPWSTR lptstrCopy = (LPWSTR)GlobalLock(mem);
	memcpy(lptstrCopy, utf16.get_data(), (utf16.length() + 1) * sizeof(WCHAR));
	GlobalUnlock(mem);
	SetClipboardData(CF_UNICODETEXT, mem);
	
	CharString utf8 = text.utf8();
	mem = GlobalAlloc(GMEM_MOVEABLE, utf8.length() + 1);
	ERR_FAIL_COND_MSG(mem == nullptr, "Unable to allocate memory for clipboard contents.");
	LPTSTR ptr = (LPTSTR)GlobalLock(mem);
	memcpy(ptr, utf8.get_data(), utf8.length());
	ptr[utf8.length()] = 0;
	GlobalUnlock(mem);
	SetClipboardData(CF_TEXT, mem);
	CloseClipboard();
}
String DisplayServerWindows::clipboard_get() const {