At the last minute, having already signed an agreement with Twitter in which he agreed to waive due diligence, Elon suddenly called a stop to the sale claiming an acute interest in whether greater or fewer than 5% of Twitter accounts are bots and claiming that this random and unimportant statistic was central to his decision to make the buy offer. He now says the sale will not proceed until Twitter provides some kind of "proof" that less than 5% of Twitter accounts are bots.
Twitter is not interested in providing this information and it's unclear how Twitter is supposed to go about obtaining an exact figure with any confidence anyway. Providing it is also, allegedly, not required by the language of the agreement in which - again - Musk already waived due diligence. They have said that they fully intend to enforce the agreement, though - by which they mean, the agreement says that if for any reason Musk backs out he has to pay Twitter something like $1 billion and they will pursue that.
I'm not aware of any developments since all that came out - except Elon declaring himself a Republican because Democrats are meanies in order to preempt that whole horse-for-a-wank scandal dropping, and Tesla's stock taking a huge hit from which it still hasn't recovered, forcing Elon to restructure the financing of his buy offer.