How is Nibbana unconditioned?
The practice of the eightfold noble path leads to the experience of nibbāna, just like the act of adverting the mind to the eye door leads to seeing light. Light, the object of seeing, is saṅkhata (conditioned), but nibbāna, the object of supermundane consciousness, is asaṅkhata (unconditioned). So nibbāna isn't the result of the eightfold noble path, the experience of it is.