@szbalint If it is "essential to the service" apparently they can refuse the service.
It simply doesn't make sense to me either. If you want to log in, it is practically impossible to do without the use of cookies. But much of the other things that people (at least people in the know) would like to be able to opt out of, are not essential.
"domain privacy service" is *not* essential to the service. You shouldn't be opting people *in* in the name of complying with GDRP.