Google does not provide a standard .iso file. Instead, it provides a , which functions similarly for creating bootable USB drives. Prepare for installation - ChromeOS Flex Help
Chrome OS Flex is a version of Google's Chrome OS designed to run on older computers, essentially giving them a new lease on life. It's a free and open-source operating system that provides a streamlined, secure, and easy-to-use interface, perfect for basic tasks like browsing the web, checking email, and streaming media. Chrome Os Flex Download Iso 64-bit Offline Installer