I'm not sure if it's the whole social media, but X (formerly Twitter) now discourage you to share links. Yes, apparently attaching a URL will rank you lower in algorithm.
X/Twitter is the confirmed case, but even others sites have dropped referrals dramatically as algorithms shift.
There's a reason everyone is pushing direct-to-email newsletters.
LinkedIn is also known for down-ranking posts with links. That's why you'll see people posting a URL in a separate comment on their own post.
These social networks are "on the Internet" but they are not "on the Web". The Web is strengthened through linking.