I don't know if it would mean a western response beyond verbal condemnation. I've studied some history but don't have the training to see the currrents at play.
China's star is rising after the 'century of humiliation', of which the West bear a considerable responsibility. Britain's behaviour towards China in the past has been reprehensible and the repercussions are still going on.
Don't know if direct conflict there = WW3.
I suspect, and it's only my view, that China is not yet ready to take Taiwan. But they dislike the West strongly for both historical and cultural reasons (the Western and Chinese political systems are incompatible). However the West is their main trading partner and they value the trade relationship highly, which is why Trump pissing all of Asia, SE Asia as well, was a really fucking stupid idea. Still, at this point they are reluctant to risk that trade. That's also why they aren't openly supporting Russia.. Admittedly they've got both legs dangling on the Russian side of the fence, but they haven't openly gone in with visible military aid.
The Western trade reliance is partly why they are trying hard to become more self-sufficient. When they reach that point? Better people than me will have more idea. They do value stability over all though for good reason and there would be quite an outcry if they took Taiwan.
tldr: I don't know but I suspect they don't feel ready to take Taiwan yet. No, I don't think it would be WW3.