Anyone can set up and run their own server on here.
This is great for lots of reasons (outlined here: https://fedi.tips/why-is-the-fediverse-on-so-many-separate-servers/) but it also means that a small minority of servers may be run by nasty people, and potentially contain nasty content.
Fortunately, most server admins use server blocks to prevent their users having any contact with rogue servers.
If you see something bad on here, it's important to report it so that your admin can take action. Click on ⋯ and "report" to report a post.