I find this the most frustrating part of federation. So many more communities to block when so many instances can have the same sorts of community
A couple things can help:
For porn, you can uncheck “show NSFW” in your profile, it will make those posts disappear. Hopefully we can personally block instances in the future. I’m only aware of blocking individual communities and overall just not showing NSFW.
Nazi instances like exploding-heads should have already been defederated by your admin, so that’s a (lack of) moderation issue. You might have to pick a better instance with a proper blocklist.
Hopefully they can also implement a filter feature like we have on Mastodon. To exclude communities and posts with specific keywords would be immensely helpful.