var user = new ApplicationUser { UserName = userName, Email =  _protector.Protect(model.Email)...... };

var result = await _userManager.CreateAsync(user, password);

    public class UserValidatorProtectEmail<TUser> : IUserValidator<TUser>
           where TUser : ApplicationUser
    {

.....



      public Task<IdentityResult> ValidateAsync(UserManager<TUser> manager,
                                                  TUser user)


        {


                user.Email = _protector.Protect(user.Email);


                return Task.FromResult(IdentityResult.Success);


            }


...

}

services.AddDefaultIdentity<ApplicationUser>(o => {
  o.Stores.ProtectPersonalData = true;
  })
.AddEntityFrameworkStores<ApplicationDbContext>()
.AddPersonalDataProtection<LookupProtector, LookupProtectorKeyRing>();