Correct me if I'm wrong; in a classic apple way the phones are not reeeeally dual sim. You have one regular nano sim slot (as we are used to) and a second eSim (it's not a slot, it's baked in). To use the eSim your country and provider must support it. So far only 10 countries in the world support this...so it's not really a dual sim phone.
https://appleinsider.com/articles...

Correct me if I'm wrong, details are always spare so soon after the keynote.