I take it that Dual SIM card use is not available in US

DUAL SIM is available on iPhones in the US and it is composed of One Physical SIM and One eSIM. This will have two lines active at the same time. If you are talking about Two Physical SIM card models then those are not sold in the US.

Axel F.

If the iPhone is unlocked the eSim can use a different carrier than the physical sim.

See here: link-> How to unlock your iPhone for use with a different carrier - Apple Support