GTK4 Feature Request: gtk_window_set_drag(on)/gtk_window_set_drag(off).
Since GTK4 has decided to base their library on top of wayland, a couple of X11-related API calls became deprecated. For instance, gtk_window_move() is among them, since it relies on information which Wayland withholds, beause of security reasons. (Good choice)
For undecorated windows, however, this makes it next to impossible to move them.
My suggestion would be to add some sort of API call, which tells the window manager "this window wants to be dragged along with the pointer device NOW".
Something like
gtk_window_set_drag(GTK_WINDOW(win),TRUE); // for drag gtk_window_set_drag(GTK_WINDOW(win),FALSE); // for drop