The Republican Party of PA, who are the majority, has the lawsuit against the PA Secretary of State and it is started with the SoS is ignoring the law the legislature passed regarding deadlines and the PA Supreme Court changed the deadline from what the law specifically said to 3 days later. The Bush v Gore opinion specifically says “in a presidential election the clearly expressed intent of the legislature must prevail”. SCOTUS could give a final ruling that any ballots that were received after the deadline are invalid and counties were supposed to keep the ballots separate based on when received per previous SCOTUS advice and instructions the SoS sent the counties. Problem is that no one can verify that that is being done, according to Alito’s opinion he just gave.

Now regarding the state legislature selecting electors, some states do have laws regarding the criteria they are supposed to use for that. I believe it is MI that has one saying electors picked have to be for whoever won the state’s popular vote.