When someone says "the UN did X" what really happened 90% of the time is that countries meeting at a convention which has been organized by the UN (and I do just mean organized, the decision to have the convention in the first place was again 90% taken by countries at another event and so on) decided that they'll do X

The UN doesn't really have any power to do anything, it's just a way to organize countries working on a series of topics in such a way that the staff and infrastructure needed to facilitate meetings are already in place instead of every new thing requiring a whole set up phase