@weiming I’m not even sure it really exists! Hootsuite ran an experiment a few years back and this is what a lot of people seem to be basing everything on. The LinkedIn algorithm has changed multiple times since then and LinkedIn certainly do not discourage linking. They have help articles on placing links in posts.
The Hootsuite experiment:
https://blog.hootsuite.com/linkless-tweets-experiment/
LinkedIn explaining how to add a link to a post:
https://www.linkedin.com/help/linkedin/answer/a525301