It’s not states rights, but a federal law, regulation, or whatever the eff it is. Federal govt says you must follow epa, or carb. No other options

https://theconversation.com/why-california-gets-to-write-its-own-auto-emissions-standards-5-questions-answered-94379

Clean Air Act empowers the EPA to regulate air pollution from motor vehicles. To promote uniformity, the law generally bars states from regulating car emissions.

the Clean Air Act …. requires the EPA to grant California a waiver so it can continue to apply its own regulations

Other states can’t set their own standards, but they can opt to follow California’s motor vehicle emission regulations