Based on this ruling, the president would have absolute immunity involving all official acts. Overthrowing an election stealing classified documents are not official by any means. He should be hammered for this, no two ways about it.
However, we’re faced with a broken bad SCOTUS who can twist rules any which way it wants, so if Donald Trump actually had a political opponent murdered, he could argue that it was for the sake of the country and this Supreme Court could conceivably grant him that that was an official act as commander-in-chief.
And there’s no guarantee that the Supreme Court will be consistent. They could be willy-nilly hypocrites, on how they approach what’s official and what’s not, especially if Biden did it and then “oh well, he was out of bounds”.
So for President Biden, based on this ruling I suggest that he’d have Trump arrested as treasonous and that he suspend the Supreme Court, dispatch law-enforcement to apprehend all conservative justices, and take them into custody for violating the constitution and he could call it an official act. “I’m protecting the country and the constitution from fascist elements, trying to undermine the country and the constitution”.
Now think about it, Biden is very unlikely to do this. But now put Trump in his place. He’d fucking do it in a heartbeat, If he thought he could get away with it if he had the supreme court, backing him. My best guess is that SCOTUS would bend over backwards to accommodate him. You might ask if there’s a bridge too far and I say in this climate it’s doubtful.