How to effectively dispose unmanaged resources?

// UserService and BookService are scoped services. Are these unmanaged resources?
public class UserService : IDisposable
{
    private IBookService _bookService;
    private IUserRepository _userRepository;

    public UserService(
        IBookService bookService,
        IUserRepository userRepository
    ) {
        _bookService = bookService;
        _userRepository = userRepository;
    }

    // ... methods

    public void Dispose()
    {
        // is it effective to use Dispose like that?
        // are _bookService and _userRepository unmanageable resources?
        _bookService?.Dispose();
        _userRepository?.Dispose();

        // is it needed/effective to set those to null?
        _bookService = null;
        _userRepository = null;
      }
}

// UserRepository is scoped
public class UserRepository : IUserRepository, IDisposable
{
    private readonly DbContext _context;

    public UserRepository(DbContext context)
    {
        _context = context;
    }

    // ... methods

    public void Dispose()
    {
        // is it effective to use Dispose like that?
        _context?.Dispose();
        
        // is it needed/effective to set it to null?
        _context = null;
    }
}