It's virtually impossible to sideload anything on an iOS device without extensive developer know-how; but for Apple itself to do a targetted attack, would be a trivial task.
Android is the privacy heaven by comparison.
It's relatively trivial to get started with F-Droid and Aurora Store, and then you can install whichever apps you need, without providing any identifying information system-wide, without needing anything beyond the Android device itself.
No PCs, no mandatory 0days, no exploits, no specific software/hardware requirements, no warez, no copyright infringement, just pure free software and a few warning dialogues from Google about the dangers of installing the third-party apps, before you can do whatever you wish with the hardware you paid for, on any Android device of any vendor.