Mustn't vs don't have to: prohibition vs no necessity

Core distinction

'Mustn't' means the action is not allowed. 'Don't have to' means the action is not required; you may still do it if you want or if the situation calls for it.

One contrast pattern, two meanings

EN: You mustn't [do X]; you don't have to [do Y].

Example: You mustn't share the production data, but you don't have to anonymise the synthetic sample.

DE: Du darfst [X] nicht; du musst [Y] nicht.