I agree on the latter point, but I think it's unfair to say the UN doesn't "do stuff". A lot of the time they partner with govs to deliver the below, but they're frequently the provider of last resort too:
UNHCR (High Commissioner for Refugees): delivers shelter, food, and protection to millions of refugees and internally displaced persons.
• WFP (World Food Programme): feeds over 100 million people annually and won the Nobel Peace Prize in 2020.
• UNICEF: runs child vaccination and education programs across the Global South.
• WHO (World Health Organization): leads responses to global health threats (like COVID-19, Ebola, and now mpox and cholera outbreaks).
That's fair, but I would say it's not really the UN that does those things, it's the countries that sponsor those programs. Saying otherwise implies the UN is some kind of distinct body with its own interests, which it is not. It is just a medium through which countries interact.