It’s not unconstitutional. The designation of electors is left up to the states. They can set up the votes any way they want.
It goes against the intent of the Constitution, but that’s not illegal.
The stuff hilighted in the excerpt from the 12th Amendment in previous post makes it clear that the states didn’t give themselves the constitutional power to give all of a state’s electoral votes to whoever wins the plurality of electoral votes for that state.
"Article I, Section 10, Clause 3: No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State [emphases added], or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay."