If the site has been indexed via any SEO analysis tool such as this - https://app.neilpatel.com/en/traffic_analyzer/top_pages, then top content can be found via backlinks and shares (note that they aren't very accurate and depends upon being indexed well).
Perhaps a browser add-on which can detect shares from the share widget could be built, but I'm not aware of such and if the blogs/websites hasn't implemented such social shares it wouldn't work.