Instance agnostic post links?

Context

• https://github.com/LemmyNet/lemmy/issues/2987
• https://github.com/LemmyNet/lemmy/commit/7c2445efe73de5b701ecb7d0b90167c1a4e29a6a

As the issue is closed, the feature should be around, and it seems like it is there based on the commit. But if yes, how do we use it?