Violating the Constitution generally is not a criminal act. If it was, all sorts of Presidents would be in prison for signing executive orders that were later overturned, etc..
It's actually a good argument to be making. The prosecutor essentially is going to be arguing "Trump did something really bad and must be punished", and the legal retort is going to be just because a president does something wrong does not not make it a criminal act, and this is a criminal trial.
Easy to offer a ton of examples of unconstitutional/illegal actions ordered by other Presidents. Hell, the student loan forgiveness qualifies. Biden ordered federal employees to engage in an action the courts determined was unlawful.
This is actually a very.important point for his lawyers to bring out, even if just for PR.