Some of the evidence that Jack Smith has put together involve some form of Trump's official capacity. for instance, the Times notes that one of the points of the prosecution was that Trump tried to get Jeffrey Clark installed as acting AG in the days before Jan 6, presumably because he would go along with the coup. One of the findings of the Court is that appointments like that are within the President's direct duties, and can't be used as evidence against him, even if it can be proven that the appointment was made to directly piss on the Constitution Trump swore to protect.
The Times also notes that Trump's pressure campaign on Pence is similarly protected now.