[jkic47]

Here is a link to the opinion so you can read the rationale behind the decision. I have not made it through the whole document yet, but here're some of the points I noted.

From the opinion: The President has duties of “unrivaled gravity and breadth.” ... His authority to act necessarily “stem[s] either from an act of Congress or from the Constitution itself.” ... When the President exercises such authority, Congress cannot act on, and courts cannot examine, the President’s actions.

A little later, they go on to say: "As for a President’s unofficial acts, there is no immunity. Although Presidential immunity is required for official actions to ensure that the President’s decision making is not distorted by the threat of future litigation stemming from those actions, that concern does not support immunity for unofficial conduct"

They have sent the case back down to lower courts to determine whether the acts were official (in which case he has immunity) or not (in which case, the prosecution must prove that the acts were not official).

https://www.supremecourt.gov/opinions/23pdf/23-939_e2pg.pdf