A SwiftUI List where a single item is selected across Sections.

ThemeListSelection.swift

import SwiftUI

struct Theme: Identifiable {
    let id: UUID
    let name: String
}

extension Theme {
    static let blue = Self(id: UUID(), name: "Blue")
    static let red = Self(id: UUID(), name: "Red")
}

enum ThemeCategory: String, Identifiable, Hashable, CaseIterable {
    case new
    case sister
    
    var id: Self { self }
}

struct ThemeListID: Hashable {
    let themeID: Theme.ID
    let categoryID: ThemeCategory.ID
}

struct ThemeList: View {
    @State private var selection: ThemeListID? = nil
    
    var body: some View {
        VStack {
            List(selection: $selection) {
                ForEach(ThemeCategory.allCases) { category in
                    Section(category.rawValue) {
                        ForEach([Theme.blue, .red]) { theme in
                            Text(theme.name)
                                .tag(ThemeListID(themeID: theme.id, categoryID: category.id))
                        }
                    }
                }
            }
            
            Text("Selection: \(String(describing: selection))")
        }
        
    }
}

#Preview {
    NavigationStack {
        ThemeList()
            .toolbar {
                EditButton()
            }
    }
}