Technically, both people on the ticket can be from the same state. There’s no rule against it. But there is a rule that an elector can’t vote for two candidates both from the elector’s state, so if Trump and Desantis are both Floridians, then Florida’s electoral votes can’t got to both. In a race where FL’s electoral votes are greater than or equal to the margin of victory, this could cause the Dem VP candidate to be elected along with Trump.
I understand how easy it was for Dick Cheney to become a Wyoming guy again. No one cared. But does Trump say he’s a New Yorker again just to accommodate someone else on the ticket? That seems like a distinctly non-Trump-like to do. Does Desantis say he’s not a Floridian? Desantis is a native of the state and is governor, so it would be kind of weird for him to abandon the state.
But it's not ridiculous to say Trump is from New York, he is. Wasn't his home state New York in 2016? I assume he would run as a New Yorker, if he ran again, anyway. He's lived his whole life in the City, and never been ashamed of it. I think he only made his residence Florida for legal reasons.