There is no “diplomatic solution” with regards to Taiwan. As seen in Hong Kong. What China wants, China will take. (This is an acquisition strategy the US knows well too…) Right now a majority of Taiwanese prefer the status quo. That is de facto independence. That does not mean they’d be okay with more interference from China. (It also does not automatically mean they’ll be cool with a war of independence either)
“There’s no diplomatic solution if the US decides there’s none”… way to remove the agency of the Taiwanese people with one assertion. Well done.
The fact is that deterrence is a valid posture with which to meet a belligerent. And if the Taiwanese decided a rapprochement with China was the right choice there is nothing the US could do about it. But that is not what they want.