@kaishin onPreferenceChange() did not change 😉 It always required Equatable (how would it detect changes otherwise!). What did change though, is that Anchor
no longer conforms to Equatable 😕 — The SwiftUI Lab (@SwiftUILab) August 3, 2019
I previously assumed that onPreferenceChange(_:perform:) added the Equatable requirement, but it turns out that Anchor<Value> dropped its Equatable conformance instead, as pointed out by @SwiftUILab and the official documentation.
A curious change, regardless.