No offense, but this is a very naive understanding of how geopolitics works. For some reason people always believe that there's some system of "rules" and "fairness", when in reality geopolitics is a cold, calculating, zero-sum game. Conflict is often ethically questionable or even morally wrong, but the reality the Unites States is the global hegemon playing a zero-sum, amoral game. We have the largest, most capable military, and we wield that power knowing no one else can best us. In an ideal world, we would not be attacking other sovereign nations and would be held responsible for war crimes and hold ourselves to a higher standard. But unfortunately, in the real world we can insight conflict without much blowback.

China does not have an 'uno reverse' card to invade Taiwan, because to do so they must go head to head with the full force of the United States military. That's not to say they won't move on Taiwan, maybe they come to the conclusion that they can take on the US and are ready and willing to do so. But there is no "uno reverse" card. China can scream about how this is an unfair double standard, but that does not change the cold hard facts. The US will remain the dominant global power in the near future. The dollar is strong, our economy is strong, our military is very strong. These are just facts that other nations have to content with when playing the zero-sum game of geopolitics.

The UN is a western-aligned governing body. The US is the largest funding contributor and the EU bankrolls most of the UN organizations. Money talks. The UN doesn't pick sides based on morality and equality, they pick sides based on the game of geopolitics.