What does this mean? Why does he need to tell a court that he’s going to endorse Trump?
It may have something to do with election finance laws. If he accepted money from people by claiming he was running for president, there are restrictions on how he can spend that money. He can't use the money for purposes other than his campaign, with restrictions. (I know the 100 million or so donated to Joe Biden will somehow be transferred to Kamala.) So it probably has something to do with campaign funds.
I think because he had to file to be withdrawn from the ballot.