NestedObservable

ContentView.swift

//
//  ContentView.swift
//  NestedObservables
//
//  Created by Craig Hockenberry on 7/2/24.
//

import SwiftUI

@Observable
class Group: Identifiable {
	init(name: String) {
		self.name = name
		self.options = []
	}
	
	let name: String
	
	var options: [Option]
}

@Observable
class Option: Identifiable {
	init(title: String) {
		self.title = title
		self.selected = false
	}

	let title: String

	var selected: Bool
}

struct ContentView: View {
	@State private var groups: [Group] = []

    var body: some View {
		Form {
			ForEach(groups) { group in
				Section {
					ForEach(group.options) { option in
						//Toggle(option.title, isOn: $option.selected)	// Cannot find '$option' in scope

						//@Bindable var selected = option.selected 		// Cannot reference invalid declaration 'option'
						//Toggle(option.title, isOn: $selected)

						let selectedBinding = Binding(get: { option.selected }, set: { option.selected = $0 })
						Toggle(option.title, isOn: selectedBinding)
					}
				} header: {
					Text(group.name)
				}
			}
			
			Button("Check") {
				for group in groups {
					print("\(group.name):")
					for option in group.options {
						print("  \(option.title) = \(option.selected)")
					}
				}
			}
		}
		.formStyle(.grouped)
		.task {
			for groupName in ["First", "Second", "Third"] {
				let group = Group(name: groupName)
				group.options.append(Option(title: "A"))
				group.options.append(Option(title: "B"))
				groups.append(group)
			}
		}
    }
}

#Preview {
    ContentView()
}

The solution is to bind on the option (Observable), not the property:

@Bindable var option = option
Toggle(option.title, isOn: $option.selected)

Thanks to Helge Heß for the answer: https://mastodon.social/@helge/112718741179217009