The discretion of official duty is left up to the trails court, not the supreme court. It’s literally in the ruling.
The president has always had immunity. This changes nothing.
If I order someone to be murdered in another country I can be prosecuted. If the president does it they cannot be prosecuted (if, obviously, it was for the protection of the United States). There is your example. SCOTUS didn’t give the president anything. The president already had it. Because SCOTUS doesn’t make law.