The UN is not here to enforce anything. It’s a forum for nations to talk to each other, in the hopes that a peaceful resolution can be reached. They condemn things in the hopes that this soft pressure on heads-of-state makes them reconsider their actions.

Unexploded cluster bombs will be discovered in Ukrainian dirt for generations to come — probably by farmers and children. The UN has to condemn it.

UN is irrelevant in some sense I guess but that depends on what you expect them to be. If they could enforce things everyone would leave at once. It's a place where countries can talk to eachother that might otherwise not. And that is at least worth something.

Considering that there have been no world wars since it's creation, I'd say it has a 100% success rate