That's not what the decision says. It says three things:
1) For things that are the explicit, constitutional authority of the President, all Presidents have absolute immunity. Most of these are things with little room for meaningful criminal activity, such as vetoes and pardons, and thus the only actually interesting power this absolute immunity covers is the command of the military. It's not without bounds, though; the President cannot deploy troops within American borders without invoking the Insurrection Act, application of which has only gotten more and more controversial over time and would probably backfire horribly if used without a decent reason. Or in other words, absolute immunity applies to drone strikes in Yemen, but not Vermont.
2) "Official acts" outside the scope of explicit constitutional authority may have immunity, namely in cases where authority is shared with Congress, but also in cases where prosecution wouldn't threaten to disrupt the power and function of the Executive.
3) "Unofficial acts", or acts done as a private citizen, receive no immunity. So shooting someone point-blank in broad daylight wouldn't be covered by immunity (though the President still might be able to pardon himself in such a case, we haven't figured that problem out yet).
The President doesn't have enough control over ICE to formally order the deportation of specific people, especially not citizens. It probably wouldn't even stop him from running; you'd need denaturalization for that, which can't even apply in this case, as Trump is a natural-born citizen. I won't even give talk of assassination a modicum of consideration, because it should be obvious why it's a horrible, terrible, stupid idea.
As an aside, I think it's funny how many people's first instincts to reading a headline about a Supreme Court case is to think of ways for the current guy to abuse it against le heckin' Orange Man Bad. It's not just here, being especially bad on Twitter and Reddit.