This magazine is dedicated to discussions on the federated social networking ecosystem, which includes decentralized and open-source social media platforms. Whether you are a user, developer, or simply interested in the concept of decentralized social media, this is the place for you. Here you can share your knowledge, ask questions, and engage in discussions on topics such as the benefits and challenges of decentralized social media, new and existing federated platforms, and more. From the latest developments and trends to ethical considerations and the future of federated social media, this category covers a wide range of topics related to the Fediverse.
Pretty sure that as of right now, there's no way to aggregate together different communities on different instances. Hopefully, the mods of the different communities can coordinate and direct traffic to each other or pick a "main" eventually.
Another option would be to add a "multi-reddit" type feature on the user-end to at least put it all in one feed.
Edit: P.S. You should also check out the communities on startrek.website.
Just use the one that's the largest. The same thing happens on all community based forums. Even on reddit you'd have r/athing, r/a_thing and sometimes r/at. Eventually people will keep gravitating towards the biggest one.