US military presence is sort of a paradox for Taiwan. It both protects Taiwan, as well threatens it, in the sense that China feels threatened by the US military and thus is incentivized to militarize out of self-defense.
Taiwan's geography makes it a natural fortress, and even Taiwan's own military can defend the island pretty well entirely on its own. A mainland invasion will be very, very expensive, so it won't happen that easily.
Economically, Taiwan is in decline. China basically doesn't need Taiwan for economic reasons. So the only reason to invade Taiwan, would be to appeal to the nationalist sentiment of reunification. But the chances of that happening is less than what many think, both because of the military cost, and because the CCP are actually moderates; there are many Chinese people who are far more radical, and if it's up to them then they would have launched an invasion a decade ago.
This probably sounds unbelievable, or even propagandistic, to many people here on HN. You don't have to take my word for it. See Kishore Mahbubani, ex-Singapore diplomat & ex-head of UN Security Council, who wrote a book on China.