A few years ago I made this flow chart of which Mastodon posts end up in which timelines!
So, you can see how each instance will have a different local timeline, and even a slightly different federated timeline - and you can see why the federated timeline moves so much faster than the local one, too.
This is why it's important to boost good posts and use hashtags - the fediverse is fragmented and harder to search by nature.
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