If you don't believe the rational I sketched, informed by analyses such as that by the Council of Foreign Relations[1], you can also learn more by reading directly from China's Mission in the EU about the China One principle: http://eu.china-mission.gov.cn/eng/more/20220812Taiwan/20220...
[1] https://www.cfr.org/backgrounder/china-taiwan-relations-tens...
If you want a semi-serious example, check the "Taiwan #1" gaming video on YouTube for a taste of Chinese nationalism.
Read certain declarations by Chinese ambassadors in Europe for more serious nationalistic takes.
They do see Taiwan as an internal matter, that's the problem they don't recognize this sovereignty and don't like or understand Democracy. It's like Russia with Ukraine but they'll also claim Taiwan isn't a country because even most western nations technically don't recognize them. It makes me think we made a mistake not recognizing Taiwan as it's own country back in the 90s when China was less powerful.
This is the main reason.
3 as I said, they can just negotiate and throw money at the problem; it's cheaper than fighting a war.
4 they can already buy hardware from them and was doing so just fine before US stepped in. DeepSeek seemed to do fine and China may likely surpass Western AI development in the near future
5 I don't see how that's the case when the US has very little presence in TW compared to SK or JP. Taiwan is a hair on a gorilla's right knee.