Technologies do plateau but consumers are still buying phones and many in China aren’t choosing the iPhone.
Consumers in Asia lean to Android because they tend to be more rational with spending and just want a phone that works. Android works just like iOS works but in Asia the packaging (ie the phone holding the OS) are significantly more attractive that what is available elsewhere.
Chinese brands like Xiaomi and Huawei are impressive. Many have used Android for years if not their entire lives.
Apple’s business model for the past several years has been repacking, increase ASP, and sell you services. Their model has shifted and Asia doesn’t care for it. Most view it as why spend 1,000s of dollars for the same outcome I can get, with an OS I’ve used for years, for a fraction of the price in a more attractive package? Plus, they support local - there is a huge support for local brands