The method of replacing the operating system on older PCs and Macs is called ChromeOS Flex.
If you have an old Mac that can't run macOS 12 Monterey, you can install ChromeOS Flex on it and try out what it has to offer.
There was an early access preview of the ChromeOS Flex test. Since having resolved 600 bugs, the company is encouraging individuals, schools, and businesses to download the software to "easily try modern computing with cloud-based management."
ChromeOS Flex was created by the purchase of Neverware, a company that offered an app called CloudReady that allowed users to convert old PCs into ChromeOS machines.
The operating system can be used on over 400 devices, including Macs released after 2010 with 16 gigabytes of free storage. OS Flex is free for individuals, but schools and businesses will still have to pay a fee.
The look and feel of the ChromeOS Flex is the same as the ChromeOS shipped with every Chromebook, as it's built on the same code base. There's no Play Store, OS Flex has system-level limitations that distinguish it from ChromeOS, and there's also some other limitations that differentiate it from other operating systems.
If you don't have time to install ChromeOS Flex on your devices, you can run it on a portable device. It's a good idea to test and verify the device's function. The ChromeOS Flex installation guide can be consulted for more help.