It is best not to scratch the skin of the back of the neck for adult cats, because the weight of an adult cat is about 10 pounds, which is relatively heavy. The skin of the back of the neck cannot bear the weight of the entire body, and it is easy to hurt the cat or cause discomfort to the cat, so try your best. Don't scratch the scruff of an adult cat's neck. Under normal circumstances, a cat can no longer scratch the back of its neck when its weight exceeds 8 pounds.
Tip:
Grabbing the back of the neck is an action that big cats use when moving kittens. It can give kittens a sense of security, but adult cats do not need this behavior.