Linux.com - https://www.linux.com/news/linux-comes-chromebooks-0
Chrome OS is based on Linux, but you can’t easily run Linux applications on it. That’s about to change, with Google’s Project Crostini rolling out.
Chrome OS started as a spin off of Ubuntu Linux. It then migrated to Gentoo Linux and evolved into Google’s own take on the vanilla Linux kernel. But it’s interface remained the Chrome web browser UI to this day.