Basically nobody seriously thinks it's an actual Da Vinci, but at this point it doesn't really matter. The narrative around the painting makes it a far more interesting work than any second rate actual Da Vinci could ever hope to be.
The surrounding narrative bit also worked wonders for another Da Vinci hit "The Mona Lisa". Had it not been stolen it would still be relatively obscure.
You don't even have to be an expert to tell it isn't. Compared to Leonardo's paintings, Salvator Mundi is just boring.
Unless Leonardo just phoned it in. But I don't think there is a way to tell if a work was painted by a student or by Leonardo pretending to be a student anyway.
That's exactly the argument I'm dismissing. It's not much of a miracle for the orb to transmit light as one would naïvely expect. Rather, it suggests that somebody didn't do their homework.