When was that? I don’t see when they were denied membership. They wanted into a partnership program that would’ve made them a member, Russian minded president shelved that idea, it was raised again when Russia annexed Crimea and it’s still ongoing.
“At the 2008 Bucharest Summit, the Allies agreed that Georgia and Ukraine will become members of NATO in future.”
“At NATO’s 2023 Vilnius summit it was decided that Ukraine would no longer be required to participate in a Membership Action Plan before joining the alliance.”
Though IIRC you can’t join during an active conflict. That’s sorta the thing, you need to be a member beforehand to reap the benefits. When it happens, then it’s too late. That’s why after Russian attack into Ukraine, Finland and Sweden got such a hurry about it.