There exist ActivityPub relays that are basically already filled indexes that you can connect to a Mastodon instance. This is what it says in the admin settings:

A federation relay is an intermediary server that exchanges large volumes of public posts between servers that subscribe and publish to it. It can help small and medium servers discover content from the fediverse, which would otherwise require local users manually following other people on remote servers.

Every instance has a list of instances that it is federated with (that the server sees). Feddit.de is a bigger instance than dataterm.digital, it has more users, which means that it is federated with more instances. It doesn’t mean that you can’t view the instances from here. You can paste the !community@instance.tld to the dataterm searchbar and if this community wasn’t on the federated list it now will be. That’s why more users = more posts on the All feed.

It’s very indie but I’ve actually worked on Danger Scavenger (and on this trailer a bit too!)

Maybe you would wanna add it to the list https://questlog.app/games/danger-scavenger