If that happens, it won't be a law, but a court-ordered punishment intended to force compliance. It seems that courts are allowed to do a lot of things to force people to comply with their orders. Up to and including imprisonment. Punishments given for this purpose apparently go away as soon as compliance happens. And this is a general principle, not just in Germany.

Germany probably already has a system for the government to order ISPs to block certain domains. It would be surprising if any overbearing surveillance state didn't.

It doesn't need to write new laws, they already exist and they are already enforced.

Try to access an illegal online casino from Italy, for example.

Brazil did that, so why not.

No, but plaintiff can ask for an injunction, and X may have to pay a fine.