When you use the Move/Copy tool to duplicate a sketch, if the duplicate is on the same plane it doesn’t create a new sketch layer.
If you move it to a different plane, in this case up it becomes a new sketch. You can move it back to the original spot by zeroing the offset distance.
However, I don’t want to use a third dimension. I want to mirror an existing sketch and use the rotate tool to rotate it 180deg. It still creates another sketch. What I’m trying to achieve is to create an element and multiply/mirror it within the same sketch