So which one is actually official one? I can't describe what "official" mean here, maybe the one that actually came from reddit or the one with more subsscribers or one with more activity ?
Also Why there are multiple copies of same community in different instances? Isn't the whole point of lemmy is that it is federated?
I don't think "official" means much here, but the one on .ml has 4 times as many subscribers as the next one down, so probably go there.
The whole point of Lemmy is to be federated, yes. That means anyone can set up the same community name on a different instance and be accessible to everyone. If it has more/better content or better moderation, it will survive. Maybe some people object to being on the .ml instance in the first place.
lemmy.ml is the 'original' instance. And i think the oldest by far. That's why you'll find the highest user counts there. But lots of people don't like their moderation policies. And switched their engagement to other instances. I think that's why you see lots of 'nominal members' in the lemmy.ml community, but the lemmy.world one is actually the more active one.
YMMV. And some people also don't like lemmy.world or so much centralization and also try to move away from lemmy.world so we're not completely dependant on a single instance.
I just search and browse for communities, click on all of them and see which ones are active and have nice posts and then I join those.