It's not entirely correct to say "Taiwan used to be part of China" without context.

The current ruling party has never had any strong claims on it. The old ruling party of mainland China escaped to the Taiwan island after losing a civil war to the other party. The current ruling party of mainland China has adopted imperialistic and nationalistic ideals and has decided the Taiwanese people have no right to be independent of the rest of China and see themselves as the only valid ruler for all Chinese people. All claims on the island itself are just cover for trying to quash independent groups.

https://en.wikipedia.org/wiki/Second_Taiwan_Strait_Crisis

Quemoy and Matsu are two tiny islands, utterly worthless in the grand scheme, that almost caused WW3.

Agree with the geographic take. China is trying its imperial powers in a way where they choose their own enemies. They also have maritime disputes with SEA in areas where their supplies would come from, in an attempt to seize control of their own lifelines. They've also been pumping money into various countries in the SEA despite the conflict to gain soft power over them, so that a blockade of the Straits of Malacca would be less likely to happen in the event of a conflict with Taiwan. Of course, they continue to build out other avenues to reduce if not move their reliance on such chokepoints, Myanmar and Pakistan being prime examples, aside from their whole Belt and Road Initiative.

Back to Taiwan though, TSMC is still the leading semiconductor company that leads everyone else by a far margin, and if it's under the control of one country and they deny access of other countries to it, they would be able to gain technological supremacy in a few years, provided that they continue to guard their secrets from spies, which, to be fair, will definitely intensify in such a world. TSMC's plans, though, is that in the event of an invasion, they will destroy their fabs.