Answer from David Martin, a happiness engineer from Automattic in his post – reblogging gets a refresh.
To prevent your site’s content from being reblogged, you can go to Tools, then navigate to Marketing, and finally click on the “Sharing Buttons” tab. From there, you can disable reblogging for your entire site. Unfortunately, there isn’t an option to turn off reblogging on a post-by-post basis
Actually, now that the original post gets the benefit of the reblog, all my objections to reblogging have gone away. See this from David Martin that explains why:
We made a significant change in this release by replacing the quote block with the embed block. This new block prominently displays the original author’s information and limits the content shown from the original post. Rather than replicating the entire post, only a snippet of the original content is displayed, along with a “continue reading” link that directs readers to the original post. This approach ensures that the original author receives proper credit and encourages visitors to visit their site for the full content. In essence, reblogged posts now function more like a link with additional context, rather than a complete reposting of someone else’s content.