Yeah, there's no blockchain or artificial scarcity or mining or anything like that here.
Fediverse (including Mastodon) is all traditional servers with owners who want to keep their electricity bills as low as possible, so they are incentivised to reduce energy use rather than expand it.
There will still be an impact from any kind of server, but on traditional servers it's not artificially high. No one is incentivised to waste energy on the Fediverse or Mastodon.
There's a project called @greenfediverse which is trying to encourage people to move to servers powered by renewable energy, that might be worth checking out too?