Right, seems I can prevent AI training by marking a work here in Germany (via UrgH § 44b Abs. 3). That would be perhaps something to add to (a variant of) the GPL.

Doesn't prevent training in the US and use of the trained AI and material it produces here, I guess.

Then I have to start a civil law-suit and prove that the produced work is similar enough to the the original work. That was the step that failed in the Hellwig (Linux) vs. VMWare lawsuit.