Tor is an application and technically doesn’t even has much to do with Linux itself, except that it also runs on it. Where you using a guide for installing and if so which one?

It is federated though? It’s literally the first sentence in their specification: https://spec.matrix.org/latest/

Both have their own instances: https://social.bund.de and https://social.network.europa.eu

I’m pretty sure there is no particular reason why it’s done this way. It’s just the easiest method to coomunicate upvotes across different servers. There are already a lot of ideas for doing it differently or more efficient (e.g. vote aggregation) but that requires a more sophisticated architecture:

• Vote aggregation also makes faking votes much more efficient and requires different detection methods. Of course, a spam server can also invent users or votes but it’s a bit more complicated.
• Aggregation in any form can be hard to implement because it should be flexible enough to reduce load but not increase delay or make tracking a consistent state even harder. Finding the right configuration will be difficult and go through a lot of trial and error. Should be easier though now that more people are working on the code.
• Keep in mind that Lemmy should also be able to communicate with other services across the Fediverse like Mastodon via ActivityPub. I’m not sure if there is something in the standard for message aggregation yet. It’s definitely being discussed because Mastodon, Pixelfed and Peertube all have or went thorugh the same growth problems as Lemmy in terms of scaling, spam and security concerns. If there’s a good solution it will likely come through the AP standard.