It's inherent in the design and use of the fediverse that public posts are public, and copied countless times all over the internet. I can't control what you do with my public posts and that should be fine.
There is no way to stop that and honestly I don't think it's even desirable to try.
Instead, we should be thinking how to do a better job of using our own collective data to build AIs that are informed and useful as a common good, in an open and principled way: