If Ukraine had kept their nukes Russia wouldn’t have invaded. It’s a powerful deterrent. If leaders fear being invaded they will reach for a deterrent.
The "Ukranian" nukes were sowjet. It was part of the deal that the sowjets get them back and Ukraine gets its independence. A lot of countries made that deal. And its a good one. Ukraine had never the full blueprints and capabilities to maintain them, so after a few years they would have gotten relative useless and a liability.