class MyUIViewController {
    private let viewModel: MyViewModel

    func someMethod() {
        title = viewModel.listName // Crash
    }
}

@objc(T1MyViewModel)
public final class MyViewModel : NSObject, T1MyAbstractViewModel {
    let list: MyModel

    public var listName: String {
        return list.displayName
    }
}

NS_ASSUME_NONNULL_BEGIN
@protocol T1MyAbstractViewModel <NSObject, NSCoding>
@property (nonatomic, readonly) NSString *listName;
@end
NS_ASSUME_NONNULL_END

@interface MyModel : NSObject <NSCoding, NSCopying>
@property (nonatomic, readonly) NSString *displayName;
@end

@implementation MyModel
- (NSString *)displayName
{
    if (!_displayName) {
        _displayName = [[NSString stringWithFormat:@"list-%@", [self.listIDNumber stringValue]] mutableCopy];
    }
    return _displayName;
}
@end