Oh neat, a topic involving NTR that is actually might actually be fun to engage with!
Speaking from my own perspective on what NTR is to me, if its any character that is not the one being "inhabited" by the player and whom the main bulk of the plot is centered around, its NTR. That would include a perfect clone since the clone would be a copy of the character that the player is inhabiting, but they are not in control of them and the story is not based around their perspective.
Now I'm down with that but I'd definitely say that it would warrant a tag were it included in a story.
Edit: That said, if it was a Doctor Manhatten situation where you are projecting and controlling copies of yourself simultaneously, I would not say that its NTR since you have total agency over... yourself.