You've hit the mark as far as their personal relationship. Trump's pissed he didn't get cooperation from Z on obvious Biden graft in Ukraine and then Z cozies up to Dems before the election (sort of understandable if he though Kamala was going to win).
I think Trump is letting his personal animosity toward Z to influence this way too much and him talking about it only encourages Putin.
To be honest, to me, this is turning, or has turned, into a real shit show and I think US reputation is going to suffer for a long time. As I said, I hope things work out for the best, and would love to be proved wrong.