There is the Note refactor plugin which lets you select text, press your configured hotkey/use the command palette and extract the selection to a new note. (It’s a community plugin.)
This is an extraction and not copying. You can however specify what should happen in the original note in Note link template, in your case just keeping the selection there should be doable with {{new_note_content}}.
I think the default embed may even be better for your use case than just doubling the text, but that’s up to your personal preferences.
In the Refactored note template you can specify with {{title}} where the link to the original note should be in the new note.
It supports other placeholders as well, take a look at the screenshot or even better, try it out yourself with the plugin.