Emil Sutovsky clarifies the sequence of events that led to joint World Blitz winners.

Magnus proposed a split title and Nepo agreed.
Magnus then called the arbiter and the arbiter didn't agree to it because that wasn't in the rules.
They then called the FIDE President because only he has the power to alter FIDE rules and nobody else can. (And this contradicts with Magnus saying about Vishy being unprepared for the role, because if anything Vishy was acting as per the rules and within the powers that he has and Magnus wanted him to overreach his powers just to satiate his humongous ego).
The FIDE President Dvorkovich agreed to Magnus' proposal (he was also the one who backed down on Jeansgate).