As soon as the Feds pass a law banning States closing their borders related to a specific circumstance then Fed law overrides State Law - the Constitution allows States to make emergency laws but the Constitution it is not specific on all circumstances - as soon as a Fed law is in place the State law is kaput.
The recent High Court case was not on border closures but on other sort of related aspects but not directly on the topic.
As said things have changed .

