OP is Original Poster. So, it’s kinda redundant to call it original original poster, but thats what stuck.
I also dont like all of the bots copying reddit posts to Lemmy, however it might help with search engine results. People dont want to go to Reddit because of the stupid update to the API terms, which is why a lot of them flock to Lemmy, because whether we like it or not - Lemmy is basically the same thing as reddit, except federated. If it grows, the community of Lemmy will be near identical to that of Reddit, or at least that of Reddit some years ago, and not just fediverse and OSS enthusiasts.
OOP is Original OP, so the original author of the thread. It is common in repost-subreddit like “Best of updates” to specify that “I”, “me” and so on in the post do not refer to the person posting, but to the original author