Window positioning? You cannot position the window, you cannot send a hint, nothing? So my pop-up with GTK4 will randomly be placed somewhere, anywhere, without any control. OK, GTK4 went further and also removed popups without the parent, so you hack that with an invisible anchor window and then write platform-specific code for sane platforms that CAN, of course, move the window. And let's not talk about window icons that you have to put somewhere on the file system?

It's not technically behind on window positioning. Rather, it was a deliberate choice not to support it. You can very reasonably object to that, but it is sorta a necessary measure to prevent clickjacking.