Not necessarily. Past presidents used blind trusts to put their assets and investments aside so that in theory they wouldn't be motivated by personal profit while president. It's not illegal for a president to conduct personal business while being president. It's unethical for the president to use his office for personal gain. And it is unconstitutional for the president to take money from representatives of foreign governments.

That wouldn't work here, though. Whether he holds them directly or through a blind trust, he'll know he has FB. Just because he can't sell doesn't matter, he could make decisions as POTUS that would greatly benefit FB.

I believe glaring conflicts of interests are a requirement at this point.

Maybe he'll hold a press conference with a stack of blank sheets of paper claiming they prove he's completely divested from his businesses, all while refusing to allow anyone to inspect the documents.