OFFICIAL ACTS is the key phrase.
I expect the Supreme Court to tule that official acts as President MAY afford some immunity, but it depends on what the act in question was, and therefore must be judged on a case by case basis.
Then, with the regard to the Trump case, the question becomes, was Trump calling for the protest of the Electoral College vote an official act, or not. The Supreme Court may, or may not rule on that yet. They may send that question back to the lower court to consider for now.
I don't think they are that stupid.
Because that could require them to litigate every single act a president took while in office. Every single one. We would have to set up a full time court just to have all the hearings.
No one wants to open up that can of worms.
But sure, let's drag Jimma Car-ter into court and have him charged with offenses against the security of the US by shutting down Verona. For starters.
I have a real long list.