Picker not updating UI when selection is made

Hi, I have an ObservableObject class called Category with a Published property called modList of a custom type called ModListDelegate that conforms to the Hashable protocol.

I'm trying to allow users to change which of their predefined mod lists is assigned to a given category, using a picker. The issue is that when I select an item, I don't get a tick next to the selected value, or any indication that the value is being changed. I'm fairly sure the value isn't actually changing.

Here is some relevant code:

class Category: Codable, Identifiable, ObservableObject, Equatable {
@Published var name: String
  @Published var items: [Item]
  @Published var modList: ModListDelegate?
  @Published var printer: PrinterConfiguration?
  enum CodingKeys: CodingKey {
    case name, items, modList, printer, id
  }
  var id: UUID 
  ... // initialisers and encoders to conform to Codable
}

struct ModListDelegate: Hashable, Codable, Identifiable {
  var name: String
  var id: UUID
  
  // note that the Category that initialises this struct is not the one to which it's assigned as a modList
  init(_ modList: Category){
    name = modList.name
    id = modList.id
  }
}

struct EditCategoryDefaultsView: View {
  @ObservedObject var category: Category
  @ObservedObject var menu: Menu
   
  var body: some View {
    Section(header: Text("Defaults"), content: {
      Picker("Associated printer", selection: $category.printer, content: {
        ForEach(menu.printers){ printer in
          Text(printer.name).tag(printer)
        }
      })
      Picker("Mod list", selection: $category.modList, content: {
        ForEach(menu.modLists){ category in
          let modList = ModListDelegate(category)
          Text(modList.name).tag(modList) // I have also tried this without .tag()
        }
      })
    })
  }
}

Any help appreciated, thanks heaps.