What about forces like US saying to intervene/support Taiwan militarily, also Taiwan having strong economic relations with West?

While Taiwan does a lot of trade with the west, trade with China accounts for a significant chunk of its economy as seen here. China can both blockade trade with the west and cut Taiwan off from domestic market crashing its economy. Another factor is that chip manufacturing is a huge chunk of the economy, and US is currently actively working on reshoring that. This will cut off a major export market to the west.

Taiwan is basically a proxy, military strategic position to US in Asia/Pacific.

There is no practical way for US to support Taiwan militarily. Every war game US ran they lost because Taiwan is right next to the mainland, and China can launch missiles directly from land to hit any US ships or planes before they get anywhere close to the action. It's also worth noting that China has hypersonic weapons that US currently has no defence against.

There's also a huge geopolitical risk for US here similar to Ukraine. Prior to the war nobody seriously questioned the assumption that the west had both military and economic superiority over Russia. Testing this assumption carried the risk that it would be proven false as turned out to be the case.

Now everybody around the world can plainly see that the emperor has no clothes. Russia showed that it is able to stand up to the west, and this opens a host of opportunities for countries that were previously subjugated by the west. We’re seeing more and more countries aligning behind BRICS and openly defying the west now.

Losing militarily to China right after a catastrophic defeat in Ukraine would make the situation even worse. Of course, that doesn't mean US wouldn't try since people running things there appear to be completely detached from reality.

Also separatist party? Afaik historically it was KMT people who fled to the island after losing to CPC

KMT has never actually been separatist. They just viewed themselves as the legitimate government of all China originally. However, nobody in KMT today actually entertains this notion. In fact, back in 2014, KMT almost managed to broker an agreement with the mainland government where Taiwan would have representatives in the mainland government, and would get to keep autonomous government and military. In response, US funded sunflower movement to put in DPP as the puppet government. Current DPP collapse opens up a way for KMT to restart negotiations about repatriation.