Well, now that you know about it, you can cross-post!
The way it works is just that any posts that have the exact same URL linked, are detected as the "same" post. You don't need the whole quotes or the "cross-posted from" part.
If the link is the same, Lemmy will show a clickable list to all the other posts that also have that link.
Well it shows up as a little icon, but nothing more. Its a thing that has been carried over from Boosts reddit days i think, tho I also don't really wanna switch right now tho. Maybe sometime in the future