Well, for cellular band coverage see→iPhone - Supported 5G and LTE networks - Apple. The China models have firmware that allows the PRC government to monitor some use of the phone, and restrict some usage models. Also, the iCloud servers and Apple ID servers for the CH model are located in China; for almost all other countries they are in the US and Ireland.
Apple Intelligence is not yet available in China, and may never be. But the same can apply to SriLanka; the initial release of Apple Intelligence will not be supported in languages other than English this year. From Apple’s AI page:
English (Australia, Canada, New Zealand, South Africa, UK) language support available this December. Some features, additional platforms, and support for additional languages, like Chinese, English (India, Singapore), French, German, Italian, Japanese, Korean, Portuguese, Spanish, Vietnamese, and others, will be coming over the course of the next year.
Perhaps the biggest difference is the China model has 2 NanoSIM card slots, and the US is eSIM only, and has no support for physical NanoSIMs. In Sri Lanka the only carrier that supports eSIM is Dialog.