gtk_window_compute_hints() adjusts base_width/base_height incorrectly.
(Filing this as a new bug in the hope that it can be fixed without fully
fixing bug #68668, though I have no idea how.)

  if (geometry_info && geometry_info->widget)
    {
      GtkRequisition child_requisition;

      gtk_widget_get_child_requisition (geometry_info->widget,
&child_requisition);
      
      extra_width = widget->requisition.width - child_requisition.width;
      extra_height = widget->requisition.height - child_requisition.height;
    }
  
  if (*new_flags & GDK_HINT_BASE_SIZE)
    {
      new_geometry->base_width += extra_width;
      new_geometry->base_height += extra_height;
    }

Suppose in your toplevel window you have a widget on which geometry hints
are set, and to the right of that widget you have another widget which has
a positive requisition height. This code adds that requisition height to
base_height, which is wrong. It should only add the requisition height of
widgets that are above or below the geometry widget in the layout of the
window. The effect from a user perspective is that the window manager
reports fewer rows than there actually are. Switch everything up and you
have the same problem horizontally.