The mastodon.social server is currently under a heavy DDOS attack and may not work properly.
The 12,164 other servers on the network are unaffected.
This is part of the reason why federated networks are a good idea: if one server goes down, the others work fine.
The more spread out we are on small and medium sized servers, the harder it is for anyone to take down the network because there's no obvious target.
There are also many other reasons why federation is good: https://fedi.tips/why-is-the-fediverse-on-so-many-separate-servers