If Satoshi Nakamoto will indeed sell some of his BTC, it will create panic in overall market because he is holding millions of BTC on his wallet, It's enough to dump the market to the starting price of BTC. But I guess he will not do that because someone can track him in case he cash out his BTC to Fiat since many eyes are watching on his wallet address since the beginning.
But I do not think that Satoshi Nakamoto will sell some of his bitcoin in just one order. I think he will send his bitcoin to reputable exchanges without having KYC, and get the money to the other forms. But I think he already cashes out his some bitcoin to enjoy what he has. He can use the other services available on the dark market, so they can not track or watch on his wallet. I am sure he can sell his bitcoin without we know if he is Satoshi Nakamoto or other people.