There is something that Twitter does right: its terms and conditions that you didn't read made you agree to allowing your posts to be shared and shown within the Twitter services. Because of this retweeting, or them showing your post in a search and even publicly, is allowed and not copyright infringement. This covers embeds as well. Because we all are used to this, we sort of assume other people's short posts are available to be shared and shown elsewhere.

On the fediverse we forget this. I've never seen a server with this in its sign-up conditions. Almost nobody has specified the copyright status of their posts and almost everybody assumes a cc-by license, allowing any kind of reproduction as long as there's attribution. So everybody just happily boosts, repeats. re-shares or re-notes.

I invite you to specify the license you expect on your posts. I have set cc-by, a long time ago, allowing any re-sharing as long as there's attribution. A boost, re-share, etc naturally has attribution, so it is ok. Other options are on the creative commons site, e.g. to include non-commercial clauses (disallowing sharing on twitter), non-derivative (disallowing editing, or even quote-tweeting possibly, maybe even indexing or AI learning). Maybe you even want to keep full copyright preventing all re-use. But this is not currently supported in the systems unless you make all your posts followers-only.

Some projects like Pixelfed and Peertube allow setting this copyright status on each separate post. For others I advice you to put it in your profile.

As always, the legal default is that the author retains full copyright control. Anybody implementing fediverse software should assume if no copyright license is specified, the author only allows publishing the post on its own server. These posts should not be shown in public timelines to unaddressed users. And no-one can boost, repeat, etc, them. Or collect them.