What people fail to understand about dynamics between countries, is ultimately there is no supreme court or arbiter of truth. The UN doesn't have authority over any powerful country (or non powerful country for that matter).

People seem to have this concept that there is some supra national legal system, or even moral system that can hold a higher truth than what powerful countries want, but there isn't. When it comes to geopolitics, the biggest and most powerful sets the rules and lives by them (or not). The USA has zero motivation to do something the UN wants it to do, if it doesn't itself want to do it. No one is going to hold it to account.

Ultimately - whoever controls the violence can set the rules. For the last 80 years that's been the US. Maybe that is changing, but not quite yet.

The UN isn't an international democratic institution. For the last 20-30 years it's been a powerless theatre. And it didn't have much power before then either. Because ultimately, whoever has the most nukes and the biggest army rules the world.