However, as one who's moved from an iPhone to a Nokia 8110 with KaiOS, which I in no way argue is as secure as iOS:
It has less on it. It has far less on it. It has my phone calls, a handful of text messages, and while it has email access right now, I'm experimenting with if I actually need that, or can remove it (leaning towards removing it). And my calendar.
The camera is horrible, so I just carry a pocket digital camera with me now if I care to take photos, which don't end up on the phone.
If I don't give it wifi privileges (which it currently has, but I've been running with wifi off and cell data off to see how that works, and the answer so far is "quite well"), there's simply not much it can really do to my accounts or network.