It's not. Because unlike people like you, who think they are clever and have found loopholes where there are none, the guys calling the shots actually know what they're talking about. Nobody is banning the letter Z in general. Only someone like you would come up with that nonsense. What they're banning is the symbolic use of the Z as shown by the Russians to rally protests or organise something in Germany with.
You ought to refrain from commenting if you have nothing worthwhile to say or - as in this case - have no fucking clue what the legal procedures are and what's actually being discussed.