Child sex abuse, for starters
[citation needed] - but like, an actual one. I know this is a popular conspiracy theory at the moment.
But if you want to dig further, you should look at the timeline of the WHO's actions and see how slow they were to recommend masks, recommend border closures, and declare a pandemic, then ask yourself if they helped or hurt our efforts to contain COVID throughout 2020. No citation is needed for that, it's all in the public domain - their press conferences and their Twitter.
Even if they don't fit that definition, they're a broken and grossly incompetent organization that covers up their own criminality, with no mechanism for accountability.
Let it not be forgotten that some of the finest wires of the Cold War came down to the delays in international diplomatic communications between Washington DC and Moscow due to the need to relay messages via embassies.
People have gotten so used to an international power structure with high speed communications and well defined diplomatic channels that they mistake the purpose of these organizations for their effectiveness. The alternative is a lot worse.
It was also the League of Nations failing to live up to it's principles when Japan invaded Manchuria.
The UN was a dream to try and resolve things in a multi-laterial world, and sometimes early on was effective (See Korea). after the debacle of the Korean War (Moscow boycotting rather then using their veto), the progress in the cold war was almost always bilateral. (not always though).
In it's current form, it's useful - but I think the WTO / World Bank and the Red Hotlines have been far more useful.
Isn't the only way to make UN more efficient to make nation states more efficient?