Is there a hypoallergenic cat breed?

Not really. The protein that triggers most cat allergies in humans is Fel d 1, produced in saliva and sebaceous glands and spread through the coat during grooming. Some breeds (Siberian, Balinese, Russian Blue, Bengal, certain Rex breeds) produce less Fel d 1 on average, but “less” is not “none,” and individual cat variation within a breed is bigger than the difference between breeds. For mild allergies, low-Fel-d-1 breeds plus regular brushing, HEPA filtration and washing soft furnishings can make co-existence workable. For severe allergies, the conversation is with an allergist, not a breeder.