PureOS is a free distribution.
It is required to not contain any proprietary software.
However, if the screenshot at https://pureos.net/ is to be believed, the web browser uses duckduckgo.com as its search engine. And this is a proprietary web page which runs proprietary JavaScripts.
It is possible to replace this with https://duckduckgo.com/lite/, or a different search engine or program altogether.