Hello, @Pites,
Actually, the duplicate content issue is not coming because of our theme. The error is related to the content you add on your product. Usually, this kind of error appears when you copy the content from your site, other pages or from the other site and then you try to index your site on Google Search Console and it will find the issue and throws an error. That’s why on every page of the site Google prefers to add or use unique content so the user will be entertained. It’s Google policy and you can read more about it here: https://developers.google.com/search/blog/2006/12/deftly-dealing-with-duplicate-content
Now, to fix the issue I found an article for you please go through with it: https://www.searchenginejournal.com/technical-seo/duplicate-content-issues/#close and read the complete article for a better understanding to know what is the cause of the issue and how you can fix it.
Regards 8Themes Team.