The UN really seems to be on its last legs, with Russia and the US launching the kinds of illegal wars of aggression that people swung for at Nuremburg, and just today (Saturday, 10/10/26 as I write) the news is the US Secretary of State openly threatening the International Criminal Court. I still think the 2003 invasion of Iraq was the tipping point that sent the UN on its path to irrelevance (as George W. Bush literally promised, and ironically I see the 1991 invasion of Iraq by his father as somewhat of a high point for the UN.) The US and Russia being permanent Security Council members, they appear to be completely immune to any consequences of their actions, at least originating through the UN itself.
Here is a TLDR article from “reality based analysis group“, except that I did actually read it! I will take issue with one small thing, which is the idea that France and the UK don’t deserve their permanent Security Council seats (which is probably true), but Russia does because it is a “superpower”. Russia’s GDP is smaller than either France or the UK’s. It just happens to spend a huge proportion of its GDP on its military, including maintenance of a huge nuclear arsenal, to the impoverishment of its citizens.
Anyway, the article goes through a really interesting analysis of international bodies that could possibly replace the UN. What they come up with is the BRICS group strengthened by some principles taken from something called the Community of Portuguese Language Countries.

While the UN is utterly failing to prevent its most powerful members from launching illegal wars of aggression, I still think the UN is functioning in at least three ways: (1) international humanitarian assistance and scientific cooperation, (2) relatively effective monitoring and inspection of nuclear weapons (with some exceptions), and (3) a forum for all (or nearly all) of the world’s sovereign nation-states (and a handful of contested ones) to come together and discuss matters of war and peace. Regarding #2, the IAEA is imperfect because while it has autonomy to conduct surveillance and inspections (as I understand it), its enforcement mechanism is to refer violations back to the Security Council. It is certainly not perfect, but it is the type of strong agreement and functional body we need to prevent civilization-ending nuclear war. The “US-Iran nuclear agreement” that was agreed to under Obama, while certainly not perfect, was agreed to under the Security Council framework and only failed when the US government decided to no longer abide by it. The world needs to work towards some kind of similar surveillance, inspection, and enforcement mechanism for biological weapons, and possibly cyber/AI weapons. When the IAEA exists and is at least relatively effective, it is hard to imagine those functions shifting elsewhere. It is easier to imagine biological and cyber-weapon controls being created within or alongside the IAEA using a similar framework.