A few stackoverflow questions make reference to the widely used method of using
https://www.linkedin.com/sharing/share-offsite/?url={url}
to let users share content from your site to their linkedin pages, but this results in a "something went wrong" error from linkedin or just the linkedin header logo on a blank page when used with any URL, percent encoded or otherwise.
The developer docs point to an oauth2 method of sharing, but that's total overkill for a share button on a website.
Was there an announcement? I can't find any and lots of websites (Youtube, NYT, ABC(AU)) are currently using this method of sharing including, ironically the very Microsoft developer doc that instructs you about oauth2 sharing.