They aren’t the same, you’ll see many communities with the same name in different instances. I’m still a newbie here, but what I do is to follow only the most popular one.
Remember that most instances are federated and some users or mods from any of the communities in different instances will make reposts from that communities on other instances, so there’s a possibility you’ll see a lot of duplicated posts.
Give Thunder a try: https://github.com/hjiangsu/thunder