And yet the US has been rushing to put nuclear warheads back on their cruise missiles at the same time as they send one of the few large Ohio cruise missile subs they have to South Korea. They also hinted that one of the reasons for leaving the INF Treaty, and taking measures including putting nuclear warheads on cruise missiles, was the increased availability of Chinese SRBMs and IRBMs in the Pacific.
As for the US not using nukes in non-nuclear conflicts, like others here said, they used them against Japan in WW2, and the US is the only of the major nuclear powers which does not have a non-first use policy even today.
American nuclear attack still seems very unlikely. Japan didn't have nukes.
US oligarchs have way too much to lose to allow some insane nationalists into killing them all just so that US can have a minimal chance to make itself slightly larger.
I mean, not even the likes of Medvedev have actually argued for nuking Ukraine as part of the offensive, and Ukraine is a non nuclear state. What nationalistic or fascistic US netizens say is not reflective of reality, and US isn't gonna begin an attack on Taiwan using nuclear weapons when they haven't even tried using conventional force. At that point, US might as well hit all of China at once with nukes, the result will be the same.
In its entire history, America was never a risk taking country. They didn't go to war with anyone that had anywhere near equal means or even the upper hand, preferring subterfuge and outlasting, even against much inferior foes such as Iran. That makes America different to the other ultranationalist regimes in the 20th century.
The idea of a Taiwan invasion in the first place is rather OOC for US, a nuclear strike during the start when no US home territories are under threat even more so.
For now, unless China dramatically reduces it military to the point where US thinks it can pull off a bloodless annexation using covert troops, I think America is most likely to simply provide economical and some amount of equipment aid to anti government fighters, but that's it.