Data does stay on iOS devices after deletion via keychain, and if the developer so chooses, they can sync your data at all times on their server to make sure it

Data does stay on iOS devices after deletion via keychain, and if the developer so chooses, they can sync your data at all times on their server to make sure it never, ever, goes away. There is a rich tradition of extracting private information off of mobile devices. It's one reason why free apps are pushed more than equivalent websites all the time (ex: reddit, imgur) , because the dataset for adtech is far more richer. Some databases and system APIs are under a user alerted permission, but that isn't unique to an app store or review, it's an OS implementation detail. Same with sandboxing apps. You have little access over running a network filter on iOS devices, and apple has had a history of rejecting VPNs that act as so. You can still have all that you put on your list, but without an app store.