You have many correct answers. Here's an explanation.
achieve - requires a direct object. So, the target has not yet achieved - is incomplete. It would need a direct object (which doesn't make sense with "target").
The target - is probably the direct object. He has not yet achieved the target. That's in active voice.
It's possible tp make a direct object function as the subject, by putting it in passive. (the) Target has not yet been achieved (by him). The subject of a sentence in active voice becomes the agent in passive voice, but stating the agent is optional).
The -- is not strictly required in front of "target" in this specific passive voice sentence, because it's commonly said in the military, which often removes unnecessary words (ones that are clear from context). This is a very rare exception. It does not apply to most other nouns (The goal has not yet been achieved. THE must be there).
Note though that in active voice, most native speakers would say "the target".
studied linguistics and English grammar; native English speaker. four foreign languages to varying degrees of competency.