This is a good example of how copyright’s continuing obsession with ownership and control of digital material is warping the entire legal system in the EU. What was supposed to be simply a fair way of rewarding creators has resulted in a monstrous system of routine government surveillance carried out on hundreds of millions of innocent people just in case they copy a digital file.
This is actually a great question, in the context of the Fediverse.
Usually, every social network or forum has in their ELUA that anything you post is theirs, and you can’t do anything about i.e Reddit using your data to train AIs.
Hlwever, here, we’re on private instances of regular people. We can make our own rules, can’t we? If an instance would say that anything you post is copyrighted by the author, i.e by CC, would it be enforcable if someone would decide to scrape (or repost) the content for profit?