Im seriously trying to work with you here. It’s very clear when I said “full autonomy” I did not mean only a “high degree of autonomy” as was the case with Hong Kong. Please listen to what I said and don’t get side tracked by imagining how a made up solution that you invented is doomed.
There’s no diplomatic solution if the US decides there’s none to be had and doesn’t even try. Diplomacy fails at times but putting in a serious effort to resolve conflicts peacefully is almost always preferable to the hardships of war. Even if you think the PRC is belligerent it’s worth actually trying.
That’s why Taiwanese people prefer maintaining the status quo. To them it seems like the best of the bad options available to them as long as they have no control over what the PRC or US does.