Only thing that works is: Dragging a Task to become a subtask of a task that already has subtasks. everything else just shows a blocked sign (see annex).
Additionally Drag and Drop has become less intutive to use since last update. The differnce in cursor location for getting that small blue line to just rearrange the order of tasks or getting this blocked sign because I'm "selecting" another task is very minimal. So much so, that I first thought drag and drop was broken as a whole.