According to this comment from 2023, most laptops are made by Taiwanese companies: https://news.ycombinator.com/item?id=36651016 I don’t know for sure, but if I read that comment correctly, those six companies are turnkey suppliers for the large computer brands.
Granted, it doesn't really matter from a security standpoint unless those subcomponents are ICs of some sort. Then again, there's probably some really clever ways to backdoor stuff even using "dumb" components.
It'd be nice if consumers had options for end-to-end supply chain assurances though.