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?

This has likely happened because the german government created the social.bund.de instance earlier this year

The instance is almost 3.5 years old btw, which you can easily see from the instance admin account @itteam@social.bund.de. It just wasn’t used by many government departments at the time, mostly the data protection agency and the BSI. The @ltrlp@social.bund.de account itself is pretty old too. It dates back to before the whole Twitter debacle. I guess that’s also part of the reason why they decided to go full Mastodon, since they already have a lot of experiences with it.

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