I have an old chromebook with no os on it. When i boot up the chromebook with my ubuntu iso inside, i just get a message that says “the device you inserted does not contain chromeos” i cant find any turorials on what to do after this. Any help would be appreciated.
there’s a URL on the screen you posted that literally tells you how to restore ChromeOS. After you do that, you can follow the documentation here to change your OS to whatever you want.