I guess it comes down to how dependent on Taiwan's chips the US actually is (I don't know the answer to that).
The US isn't dependent on Ukraine and it's pressuring them to hand over land. If it turns out the US isn't dependent on Taiwan it could show similar indifference if China were to attempt to take it.
In practice, probably yes, officially probably maybe. Giving a security guarantee would allow Taiwan to do provocative things, so hence, why there isn't a formal one.
If it actually came to be today, I guess the US would at-least offer token support. To (a) embargo China, (b) ensure chip facilities Taiwan aren't surrendered intact.
Both of which doesn't require winning a conflict, just making it painful.
'Security guarantee' conjures thoughts of defending a population and its cities from destruction, whereas what it actually means is the opposite: to ensure all items of value are fully destroyed before they're taken.
And without it, Taiwan would probably press harder for nukes.
The world is largely dependent on TSMC, not only for the latest GPUs but also for embedded chips that we keep putting into everything from cars to toasters.
For me the questions isn't whether the US would help Taiwan because we're dependent on them. I wonder whether we actually have the backbone to step in militarily at all, and whether out military is as combat ready as we like to think they are.