Can you elaborate why do you think that export of NSOs software would be against US law, preferably which specific law?
My first assumption is that the act isn't covered by any US law at all. For some analogy, the murder of Jamal Khashoggi does not violate any US law as the many US laws regarding murder (i.e. the separate criminal statutes of each of the US states plus any federal laws that may apply) do not regulate acts done by Saudi citizens to Saudi citizens in Istanbul.
So the question becomes not about legality but about policy - whether the act harms US interests. And arguably selling of arms and tools by US allies (e.g. Israel) to US allies (e.g. Saudi Arabia) is not against US policy and thus there's no grounds to apply any sanctions - now, if NSO would sell the same things to Iran, that would be a different issue.
USA could have standing if NSOs tools have been used to hack journalists in USA - but this is not what this article is about. If NSOs tools have been used to hack journalists in Saudi Arabia or United Arab Emirate or Mexico, that's not a violation of USA laws; and if this has happened according to the legal permissions of the respective government (no matter how lax or arbitrary granting these legal permissions may be) then it's not a violation of any law; if we look from the purely legal perspective and not the moral one, it's perfectly legitimate for sovereign states to make laws that abuse their journalists as much as the state wants as long as it doesn't rise to the level of crimes against humanity. Almost any act or argument against a dictatorship abusing their people is inherently political, not legal.
One incident where NSO may be in hot water is the hacking of Rania Dridi described in the original article if the events happened in London (it's unclear to me from the description) - then this may be cause to assert that NSO are complicit in violating UK law (but not USA law).