Capacitor on iPhone Duo

Start here, because it is the thing that will waste your afternoon otherwise:

WebKit 27.1 implements Device Posture and Viewport Segments, but both sit behind an experimental flag that only Safari can set.

A Capacitor app runs in a WKWebView it does not control the flags of, so navigator.devicePosture, the device-posture media query and the env(viewport-segment-*) variables are all absent there, while the same page in Safari on the same device can see them. Feature-detect rather than assume, and plan for both to be missing.

So the web platform gives you no fold awareness on this device out of the box. What it does give you is most of what matters. Work in two tiers.

Tier 1 — works today, no native code

Trust safe areas, and never assume symmetry