Maybe there is a simpler UI for that, and UX wise even show the first 2 posts of the thread so you can quickly scroll to see if it’s relevant, many times you can’t judge the quality by that first message.
Also think it takes a lot of vertical space and has icon on the left and right to do the same action.
Consider trying to show something like “Expand 6 more posts" simply as a link styling at the end of the last message to expand.
Similar behavior is in Instagram read more