This compact requires the electors from the states signed into the compact to vote for the person which wins the national popular vote, even if that person did not win the majority of the votes in that state. Does this ruling affect this at all?
This decision means that the National Popular Vote Interstate Compact(NPVIC) could be more strictly enforced in states that have laws against faithless electors.
The two cases related to this decision, Chiafalo v. Washington and Colorado Department of State v. Baca, essentially centered around whether state laws enforcing an elector's pledged vote were constitutional. SCOTUS unanimously decided they were, meaning that states can implement laws designed to stop faithless electors by requiring an elector to vote for who they pledge to vote.
However, the wording of NPVIC is such that if 270 electoral votes worth of states join, then all states in the compact will choose the slate of pledged electors which correspond to the winner of the national popular vote, rather than the state's popular vote.
The text of the bill states are passing can be found here, and the relevant part of the bill:
Article III—Manner of Appointing Presidential Electors in Member States
Prior to the time set by law for the meeting and voting by the presidential electors, the chief election official of each member state shall determine the number of votes for each presidential slate in each State of the United States and in the District of Columbia in which votes have been cast in a statewide popular election and shall add such votes together to produce a “national popular vote total” for each presidential slate.
The chief election official of each member state shall designate the presidential slate with the largest national popular vote total as the “national popular vote winner.”
The presidential elector certifying official of each member state shall certify the appointment in that official’s own state of the elector slate nominated in that state in association with the national popular vote winner.
In short, the National Popular Vote Interstate Compact means states agree to use the national vote to chose a group of pledged electors rather than the state vote, and this decision allows states to pass laws that require those electors to keep their pledge.