They have to unanimously find that he falsified business records with the INTENT to conceal another crime, but they do not have to agree on what that other crime was, just that he INTENDED to do something unlawful.
I don't think it was ever proven that Trump was aware of the Stormy Daniels extortion scheme until after the election. Cohen tried to use a 96-second phone call as evidence but that turned out to be about something else.
Merchan, by allowing Stormy Daniels' irrelevant testimony, has millions of people believing that Trump had an affair with her, for which there is absolutely no evidence (beyond her allegation), some of which will refuse to vote for him because they think he is a bad man because of the affair.