Rust is certainly part of the Linux kernel, famously, and I believe also Windows and Android, if not macOS. Not a _large_ part, I dare say, but that's not the claim.
> It’s only worth pursuing an independent career path if that’s something you really want, and even if it is, I’m not promising that it’ll make you rich. Probably the reverse. For all the billionaire startup founders we read about, I can introduce you to dozens of people who, as a result of starting their own business, are the poorest they’ve ever been.