Taiwan thinks that it can make a war with the mainland so costly for the latter that it would not make economic sense to invade. This is unrelated to the US; ideology takes a backseat to making money almost anywhere in the world and the Taiwanese know this.

My dude, the entire ROC military is completely controlled by the KMT. Yeah, a military that's institutionally controlled by the status quo party is going to fight to the last man while Tsai Ing-wen and William Lai take the first flight to Japan. The government might have transitioned away from a KMT military dictatorship during the 90s, but the actual military hasn't moved away from its KMT military dictatorship roots, especially the top brass. Taiwanese separatists have a reputation for dodging conscription, so in the end, you have a top brass that's still nostalgic about the Chiang Ching-kuo days and a bunch of enlisted and conscripted soldiers who don't care a whole lot about Taiwanese separatism. There's a reason why the DPP has continuously and successfully run on "the KMT will sell out Taiwan to the CPC" in order to win seats, most recently in the 2020 Taiwanese presidential election.

There's a decent chance there won't be an invasion anyways because the KMT cut a backroom deal with the CPC.