What is the Replies feed?
The Replies feed is not a feed of posts, but of comments. Specifically, it’s a feed of comments that others have left on your posts, in response to you!
So, the feed card looks a bit different, although the behavior is the same:

Writing a response to a comment on my post
Due to LinkedIn limitations, we don’t always bring in responses to comments you’ve written on other peoples’ posts.
By the way: we recommend starting your daily 10-15 minute Aware engagement ritual, in the morning, with the Replies feed. It’s great to get the algorithm warmed up, and do some easy “comment responses” before you do outbound comments.
If you come back later in the day and need to refresh the Replies feed, which you can do up to every 3 hours, you’ll see a button at the top allowing you to do this.