Ukraine's refusal to join NATO for security guarantees

I saw news that Zelenskyy, during negotiations, allowed for the possibility of Ukraine refusing to join NATO in exchange for some security guarantees from the USA or European countries. I don't quite understand how reliable such guarantees can be and what this would mean for our country. Can such security guarantees realistically replace NATO membership from a legal point of view? How would this protect us at all in the event of new aggression?