List with multiple selections from core data

I'm trying to adjust a list so that it can have multiple selection.

It works when I use hard coded data, but when I try and use it with core data, the option to edit the list doesn't bring the checkboxes up.

Working code

struct DIMTest: Identifiable {
    let id = UUID()
    let name: String
}

struct DimTypeListView: View {
    let contacts = [
        DIMTest(name: "John"),
        DIMTest(name: "Alice"),
        DIMTest(name: "Bob")
    ]
    // 2
    @State private var multiSelection = Set<DIM>()
        
    var body: some View {
        NavigationView {
            VStack {
                // 3
                List(contacts, selection: $multiSelection) { contact in
                    Text(contact.name)
                }
                Text("\(multiSelection.count) selections")                
            }
            .navigationTitle("Contacts")
            .toolbar {
                // 4
                EditButton()
            }
        }
    }
}

but when I adjust the code to the below to load from core data, I don't get the checkboxes

    @SectionedFetchRequest var dims: SectionedFetchResults<Bool, DIM>

    init(dType: DimType) {
        _dims = SectionedFetchRequest<Bool, DIM>(
            sectionIdentifier: \.favourite,
            sortDescriptors: [NSSortDescriptor(keyPath: \DIM.favourite, ascending: false), NSSortDescriptor(keyPath: \DIM.name, ascending: true)],
            predicate: NSPredicate(format: "dimType = %@", dType)
        )
    }

    @State private var multiSelection = Set<DIM>()
        
    var body: some View {
        VStack {
            List(dims, selection: $multiSelection) { section in
                Section() {
                    ForEach(section) { dim in
                        Text("Name")
                    }
                }
            }
            Text("\(multiSelection.count) selections")
        }
        .navigationTitle("DIMs")
        .toolbar {
            EditButton()
        }
    }

It shows the correct number of entries, but can't be selected

If i add an onDelete, i get the delete options but only want to be able to select, not delete