I believe Asana won’t allow it natively as Rules don’t have the action to create a task. You can only create a subtask or create approval subtasks. So you’ll have to rely on other solutions indeed. You can refer to my post to find solutions that would help (“Create task” in “actions”) The Asana automation bible: all the triggers and actions from Asana, Zapier, Flowsana, Make.com
For Zapier the action will be available directly in the zap. The hard part will be the trigger because you are waiting for a specific task to be completed correct?
Does this help?