Fediverse

So/so.

You only have the option if it's your instance that you're having defederated. You cannot prevent anyone from:

• Spinning up a new instance then federating with you, then bridging the content from there to the defederated instance.
• Simply using a web-scraper and a bot to post your stuff on another instance.

The second part is basically what is happening here.

Importantly, I feel people misunderstand on a fundamental level what it means to post things openly on the internet. Your only way to prevent this is simply to not post to a site that people can access freely and without a process through which you are vetting them for whether you trust them. As in: Just like IRL when you decide whether to tell things to friends or acquaintences or well, not.

But, on the web, you not only cannot prevent someone taking your public data and copying it over to wherever they so desire, you don't even know since they could be posting it in a place that you in turn have no access to so you cannot see it there.