Trump was just being his boastful self when he said he might appear at this trial. He knows, and more importantly, his lawyers know, there’s no way for him to smooth things over after the jury heard him say in recorded sworn testimony that he felt he could get away with assaulting women because of his star status. This case is lost, and Trump and his representatives know it.
There’s no reason for Trump to testify in this politically partisan sham of a trial because he clearly and truthfully shot down all of Carroll’s accusations in his deposition. He didn’t know Carroll and he certainly didn’t rape her. Just like other suits and investigations, this case is meant to derail Trump’s return to the White House, but instead, it’s making him more popular among Republicans.