They support multiple SIM cards through eSIMs. China region iPhones support two physical SIMs with a dual sided SIM card tray.

One regular SIM plus an eSIM (which you can have many installed, but only one active at a time). I also believe some Asian markets actually have dual SIM slots. I saw a YouTube video where they swapped the little daughter board with the sim reader on it from a dual SIM iPhone into a US iPhone and it worked without issues.

I currently have dual networks setup (SIM+eSIM) and it works great. I think the battery life is slightly reduced, but that might be in my mind.

You are one of the lucky ones to learn today just how good dual SIM can be. If you have an iPhone 10S or better, or a recent Pixel, install the Truphone app, grab a T-Mobile prepaid SIM, or try silent.link, and watch your main carrier’s dead zones vanish as the second carrier automatically fills in. And don’t ever worry about changing SIMs when you travel again.

They support esim.