Google said the best approach for when you allow others to syndicate and publish your content is to make them use the rel=canonical attribute, so Google knows where the source of the article is.
Google said on Twitter "For syndication, using rel=canonical is the best approach (it doesn't guarantee only one version is shown though)." Google is saying here it helps but won't 100% guarantee that only one version of the content will be shown in Google. Google may still show a syndication partner if all the signals are not clear and consistent.
Here is the tweet:
For syndication, using rel=canonical is the best approach (it doesn't guarantee only one version is shown though). For internationalization, use hreflang instead.
— Google Webmasters (@googlewmc) December 2, 2019
We covered this before when Danny Sullivan from Google went on about this saying make your syndication partners canonical to your content.
Forum discussion at Twitter.