I do not speak Greek. I am a native English speaker. "The pizza has not lemon" is not correct for this statement. It should be The pizza has no lemon"
Am I missing something? I do not see: "...has not..." but "...does not have..." What kind of an exercise did you have? Strengthen skill, or multiple choice?
The verb ‘has’ can take ‘not’ in this way, like ‘is’ does, even when not being used as a helper verb, but it's pretty rare nowadays. It should be accepted but should never be suggested by Duolingo.