It’s no different than me sending an email to someone and then sending a request to delete it. There likely is still a copy on the email provider’s server and the recipient could have potentially backed up their emails to something outside of the email ecosystem.
Unfortunately the only way to be absolutely sure that there isn’t information you don’t want on the internet is to not share it at all. There will always be an issue of making sure every system actually deletes content when you request it. Like I said, that doesn’t stop anyone from backing up the data to another system. (E.g. Reddit archives from 2005 to now are available to download, even content that has already been deleted)
One of the problems with the fediverse is that each server keeps its own copy of the content. It is definitely a worry that bad actors push content to federated servers to get them taken down due to the content they now are storing.