Certain government offices might have historically required him to give up control of Facebook, but Donald Trump is currently redefining how much ownership of business one can have as President
I don't recall any laws being changed in this regard. Trump is only pushing boundaries that were never really there. If you dislike it, get your Congressional leaders to pass a law against it.
There were there as tradition, like most things are, for instance filibusters were mostly a tradition never laws, many things work that way under the assumption that elected official and grownup responsible people, and it was assummed no one would elect people with obvious conflicts of interest, so previously presidential candidates promised to use blind trust because they were good honorable people, Trump is none of those things, except possibly 'people'.