iOS 17-compatible SwiftUI implementation of cellLayoutMarginsFollowReadableWidth

ContentMarginsFollowReadableWidth.swift

import SwiftUI

@available(watchOS 10.0, *)
@available(iOS 17.0, *)
private struct ContentMarginsFollowReadableWidthModifier: ViewModifier {
    static let readableWidth: Double = 672
    static let minInsetLength: Double = 16

    @ViewBuilder
    func body(content: Content) -> some View {
        GeometryReader { geometry in
            let insetLength = max(Self.minInsetLength, (geometry.size.width - Self.readableWidth) / 2)

            content
                .contentMargins(.horizontal, insetLength, for: .scrollContent)
        }
    }
}

public extension View {
    @ViewBuilder
    func contentMarginsFollowReadableWidth() -> some View {
        if #available(iOS 17.0, watchOS 10.0, *) {
            self.modifier(ContentMarginsFollowReadableWidthModifier())
        } else {
            self
        }
    }
}

Example usage:

List {
    Text("Hello, World!")
}
    .contentMarginsFollowReadableWidth()