I don't think you understand what is going on here. What you are saying is that iPhones cannot download data containing a list of things to block (or do whateve

I don't think you understand what is going on here. What you are saying is that iPhones cannot download data containing a list of things to block (or do whatever with) or that Apple cannot push an update. Xiaomi phones are downloading a JSON file. That has nothing to do with backdoors or remote access. In fact that whole debacle about Apple scanning a device for child pornography works just like it: Download data from a server and do something. If that is a backdoor than 100% of devices that are online are basically backdoored. Functionally this is no different than iOS downloading a list of apps to block.