iPhones purchased in mainland China (with model number ending in CH/A) do provide options for setting per-app Internet access permissions. There are three options [0]: Off, WLAN only, WLAN and Cellular.
[0] https://old.reddit.com/r/ios/comments/aib10i/in_china_ios_al...
What? Why is this Chinese market only? This is exactly what I wanted. There are Apps I simply don't want them to touch internet.
Crazy. So they're explicitly selling crippled devices to most of the world.