Medium is a no-brainer - you can set your website's URL as the canonical URL (https://help.medium.com/hc/en-us...)
LinkedIn is good for exposure, but might hurt SEO if it gets indexed by search engines
For Medium you can reshare using the proper setup.
For Linkedin I would advice you not to reshare the full article. .I would recommend you to use Missinglettr V3. It is quite good to repurpose your content for linkedin and it won't hurt your SEO.