Also, Aircraft carriers are vulnerable to mass missile attacks, and land bases in the Philippines, Japan or Taiwan are within missile range.
An effective conventional strike against military targets on the mainland would be met with China's best conventional response.
Jumping to nuclear threats or use of a nuclear weapon shows weakness and terrible escalation management. Two traits china doesn't exhibit.
As much as nuclear powers want you to think they will use them if you resist their goals, nukes only come into play when state survival is at risk, not when belligerents pursue limited goals. The US will never pursue the defeat of China. They will manage escalation. They will pursue the limited goals of status quo maintenance and a quick resolution, which can include bombing industrial production nodes to signal that China will lose a war of attrition, forcing it to call off an attack on Taiwan.
The original post was postulating that American bombers and intelligence could destroy China's production base. If US attacks did destroy a significant portion of China's factories, and production facilities, I have no doubt the war would become nuclear.
Any US attack on China's industrial base would have similar signalling to control escalation risk. It would probably be limited to key nodes in the missile or drone supply chain rather than attacking the entire base. China likely wouldn't use nukes because they are also worried about the same escalation risks as the US. They will know the US is pursuing limited objectives. The US will probably tell them this through a deconfliction line, as well as publicly. If China does use nukes, it'll likely be limited with the goal of escalating to deescalate.
None of these decisions are easy and I agree there are significant risks. But I wouldn't rule it out, especially if the alternative is to lose a war of attrition and have your influence rolled back.