Noah's individuality focused on his ambition. His law made him overcome the limits of his cultivation level, but it also had other effects.
Noah had been unable to abandon anything during his journey. His ambition had made him keep his destruction, creation, and other aspects of his existence.
That path was far harsher than other journeys due to the width of the individuality, but Noah had managed to push it to his current level. Now, the ambition that had made him unable to leave anything behind allowed him to express everything simultaneously.
Noah's new slash wasn't exactly a new technique. It used the basics learnt during his training with Sword Saint, and it applied them to all his attacks. Noah only had to pour his ambition into his blows to manifest its effects.
The countless cuts were one of the techniques that best expressed his individuality. Noah only had to slash once to create a virtually endless number of injuries on his opponent.