What is the purpose of those amp- prefix file?
These files are used to render AMP version of the website (if this option is enabled, by default it is disabled).
You can read more about AMP here: https://amp.dev/about/websites/
Do you appreciate the support you've received today? If so, consider donating to the Publii team by clicking here; we'll be sure to use your donation to make Publii even better!