I think that immunity for explicitly delineated powers makes sense purely from a logical point of view: the constitution says the president can do a thing, therefore a law saying they can't do that thing is either unconstitutional, or doesn't apply to the president.

You are effectively implying this, but I will say it explicitly - you don’t need immunity to reconcile the logical conflict. The courts can simply find that that law is unconstitutional facially (if it is specifically directed at an enumerated executive power) or as-applied (if it is a general law that sweeps in executive conduct that falls under an enumerated power). In other words, it’s not that the President is immune from criminal prosecution for violating a criminal statute, but instead Congress violated the separation of powers when passing the law and it therefore can’t be enforced because it is unconstitutional. In that situation, this would be a defense to the prosecution, with the burden being on the President to raise and prove the unconstitutionality of the law just like any other defendant. We don’t need to invent a new immunity to protect the President against Legislative excesses.

I think that immunity for explicitly delineated powers makes sense purely from a logical point of view: the constitution says the president can do a thing, therefore a law saying they can’t do that thing is either unconstitutional, or doesn’t apply to the president.

Yea, it's an interesting one. AFAIU, the delineated powers are basically command of the military and the power to pardon. I really don't see how a Crime can generally be applicable to either of those. It's not like "commanding the army" can just become a crime.

But regulating what the army can legally do ... seems like a very natural thing. I don't know if individuals of the military in the US can be responsible under ordinary law for anything. If so, then I don't see why that would extend to the president should they order something that's obviously a crime. If not, then that's that. And again, there are probably natural exceptions to carve out regarding the very nature of military action that would lead to preposterous inconsistencies if they could possible be made generally criminal ... where again, it seems to me that you don't need immunity ... it's just the nature of the power that is amenable to falling within the meaning of legislative regulation.

Beyond all of that though ... there's the opening line of Article II:

The executive Power shall be vested in a President of the United States of America

WTF is "the executive power"?! I'm sure there have been attempts in the US to give it some shape ... but I'd also wager it's been left somewhat nebulous too, involving elements quite distinct from whatever powers Congress/Law can confer. Does that count as an enumerated power?

Otherwise ... yea I'm with you. The "official acts" thing seems more than wonky to me ... seems downright expansive. Excluding military action and whatever "fuzzy" powers may be considered intrinsic ... I'd imagine most of the executive's powers come from legislative laws. So the body conferring power can't constrain it to "not doing something criminal"??!!

I've wondered since having a brief look at the decision that the SCOTUS is playing a game here ... where they do not want Trump's trials to affect the election and are hoping to clarify this decision and what "official" means at a later date after the election.