Some examples trying to deal with this involving Mastodon (years before the Twitter Musk debacle) :

Mastodon is big in Japan, and the reason why is uncomfortable ["child porn"]

https://news.ycombinator.com/item?id=15053064

Mastodon and the challenges of abuse in a federated system

https://news.ycombinator.com/item?id=17894684

How the biggest decentralized social network is dealing with its ["]Nazi["] problem

https://news.ycombinator.com/item?id=20429465

Trump’s new social media platform found using Mastodon code

https://news.ycombinator.com/item?id=29079404