“No employee of the executive branch acting in their official capacity may advance an interpretation of the law as the position of the United States that contravenes the President or the Attorney General’s opinion on a matter of law“ would seem to rule out, say, accepting a SCOTUS ruling against the President, should he insist it was wrongly decided.
They are trying to supercede the oath to the the constitution that people in the executive take, and also to supercede the authority of the other branches.
It's as simple as that.
A court ruling isn't a matter of law - you can say the ruling was issued wrongly, and you may even be right, but you still have to follow it.
If that were the case, then SCOTUS would just invalidate the EO.
Does any law or executive order say "unless invalidated by a court"? Isn't that kind of a given?