The actions of the UN pre-vietnam war are essentially a one-off “oops we were figuring out the rules” type deal. The fact that the UN and the world at large survived the Cold War, happened in large part because all major nuclear powers had veto power, giving them a rare opportunity for open dialogue that doesn’t threaten their sovereignty. Avoiding nuclear war and/or WWIII is the UN’s Prime Directive, everything else is just a bonus. Unfortunately the only way you’ll get Putin, Biden, and Xi Xinping to sit at the same table is by assuring them that no binding decision will be taken, so that is what the UN guarantees by design.