This is an absurd lawsuit based on the plain language of the Constitution.
My guess would be that they will argue that, because the states have decided to select electors by popular vote, that it’s unfair to do it on a winner take all basis.
This could backfire, if states respond by rescinding popular votes in presidential election, and just let the legislature directly appoint electors.
If some liberal judges agree with the lawsuits, things could get ugly, with unintended consequences.
Does Amendment XIV, Section 2 require popular vote for electors, at the risk of losing representation in Congress?
States with one representative clearly be unaffected.