I doubt that these things are ever personal. People in position of power meet all the time and not necessarily with good intentions.

Trump got power, Zuckerberg got power and they meet to discuss how to proceed. Trump loses power, Zuckerberg locks down his account because the arrangement is no longer viable.

The deal itself could have been anything, maybe Trump threatening to regulate the hell of FB if they don't play ball, maybe Zuckerberg had a good idea on how to get rid of TikTok with the help of Trump in exchange of letting him do his thing. Who knows?