US and the west place a lot of strategic importance in Taiwan so they may come to the defense, but it is unlikely to be defendable for long.
We are seemingly moving towards another Cold War: China and Russia vs US and NATO.
The next step if China were to move on Taiwan, other than getting all the data and IP from TSMC's internal networks, would be to spin up a US division and assign that IP to that new corporation. And then the US should try to get as many of TSMC's employees to the US that they can.
Operation Paperclip TSMC.
Sure an important part. But lets not forget that there is a lot of knowledge in TSMC too. And China is trying to slowly buy their engineers.
Intel and AMD (now Global Foundries) both had access to same Dutch company's product and they didn't or barley managed to keep up.
The western alliance has not only rebuffed Russia, it has expanded eastwards against promises made and thus provoked the current situation in Ukraine.
What would the US do if the soviets were to expand into Mexiko? Or... Cuba? We know how that went. If the mission of NATO was to secure peace, why would they reject Russia? It makes no sense from that perspective.
The answer is that there are other reasons NATO exists and what it is being used for.
If Taiwan doesn't already have plans to destroy them in case of an invasion I'm sure they are the target of some missiles from outside the country.