This article as more information:
“The justices had in February, after President Joe Biden’s inauguration, rejected a handful of cases related to the 2020 election. In the case the court rejected Monday, however, the court had called for additional briefing that was not complete until the end of March.
“The case involved a federal court challenge to a Pennsylvania Supreme Court decision requiring election officials to receive and count mailed-in ballots that arrived up to three days after the election. More broadly, however, the case concerned whether state lawmakers or state courts get the last word about the manner in which federal elections are carried out.”
>>More broadly, however, the case concerned whether state lawmakers or state courts get the last word about the manner in which federal elections are carried out.”
This is already settled law and it is the state legislature.