Very questionable whether the Electoral Count Act is constitutional. The Constitution specifies that the state legislature has plenary power to award electors, yet the Act specifies that the governor is deemed superior to the state legislature if there is a dispute. Seems unconstitutional to me.
Yes, the Constitution specifies that the state legislatures have plenary power to award electors, and each state legislature has through statute created schemes whereby Electors are chosen by popular vote. Each state, again by statute, has designated the Governor as the person to certify the slate of Electors and to transmit the results to Congress.
So the Constitution designates the state legislatures with appointing Electors, and the state legislatures have enacted statutes directing how those Electors are to be chosen.
The Electoral Count Act is the U.S. legislature designating how Electoral vote results are to be tallied, and how to resolve disagreements.
The Constitution says that each state will appoint electors "in such manner as the Legislature thereof may direct". If the states choose to allow the voters to award electors then there's nothing unconstitutional in that. And nothing unconstitutional about states having local officials certifying elections, either. Constitutionally states determine how the elections are managed.