The two states directly involved in this ruling are Washington and New York. Both states have now been told by SCOTUS that their electors are BOUND to vote for the winner of the STATES Popular Vote results.
Both states are part of the compact to give the states Electoral Votes to the winner of the National Popular Vote, but they just went to court to FORCE their electors to vote for the STATES Popular Vote Winner.
10th Amendment for the win.
This is true, but only because these two states have current laws that require them to instruct their electors to vote for the winner of the States vote. They could change their laws to do it in a different way, but they can't do it under a mechanism via a compact between states.