I’d say our biggest mistake was even entering into the One China policy (especially after the Korea War) and not formally recognizing Taiwan’s Federal government decades ago. Like 4-5 decades ago when China was a shadow of it’s current expanding power.
Taiwan, a country we give so much for, tariffs our exports to them at around 8%. We have no friends.
I would say the big mistake was forcing Chiang to retreat to Taiwan and then recognizing the Communist government in China.
MacArthuer and Chiang Kai-shek would likely have reclaimed China but Truman shut that down. Not to be outdone Britain gave Hong Kong back and left their citizens there at the mercy of Communism. Sort of like we left our allies trying to grab on to helicopters leaving Vietnam.