I don’t really understand how Neanterdals aren’t considered human, but we can breed with them. About the only difference between the two is skull shape.
If you look at African skulls, or Asian skulls or Caucasion skulls, they also differ in shape, but I don’t think anybody here question that Africans or Asians or Caucasions are not human.
Everything else between the two groups are identical or very nearly so.
They are considered human. There were many different humans that are now extinct.
The Humans Who Went Extinct: Why Neanderthals Died Out and We Survived