My first thought too. Wouldn’t Apple still own a trademark of some kind for this word?
> The absence of a product or service name or logo from this list does not constitute a waiver of NeXT’s trademark or other intellectual property rights concerning that name or logo.
If I were the OP, I would think of another name than to pay Apple for usage of the trademark and have to place 'NextStep is a trademark of Apple Inc.' like how Apple is paying for iOS with Cisco owning the IOS trademark.