If you see a post from a @threads.net user, don’t bother replying yet—they won’t see it.
You can like the post if you want, but they won’t be able to tell who liked it from the #fediverse, only a count of how many and from how many servers.
You can repost a #Threads post here, but the original poster won’t be able to tell that it happened (yet?). They will still see anonymous likes from readers of the repost, though.