I have noticed recently that if you forget to detach the tug before applying power to the engines to begin a taxi, the engines stay idle and the aircraft does not move anywhere.
Although it should be pretty apparent that you should detach the tug before taxi, I think it would be pretty helpful, especially for people like me who are prone to forgetting stuff like that.
As of now, I would imagine the message to be somewhat like what pops up before you try and push back with the ground equipment there.
Thanks for reading!