For Mastodon server admins, a bit more about the "authorized fetch" feature.
It makes it more difficult for blocked accounts to interact with public posts on your server. It's not fool-proof as public posts can always be scraped by outsiders, but it makes life harder for trolls etc so it might be a good idea to switch it on.
It isn't controlled from the graphical interface, it can only be activated by editing a file on the server manually. There are technical details here:
If you're on a managed hosting service, don't worry about the technical details. You can ask the service itself to make the necessary changes.
As it says in the documentation, "authorized fetch" isn't on by default. According to the developers this is due to the additional resources it consumes and the possibility of breaking compatibility with instances running older software.
It's up to the admin of each instance to decide what the best balance is.