AI Write from SERP
Targeting the AI writer on certain SERP text can be done with the "write about this" option underneath a header in a source in the Research tab.
Clicking the "Write about this" button (as shown in the screenshot below) will write related text to the SERP passage under which it's selected, and utilize the entire content of the source as background context to write from.
After clicking the button, the output could be between 200-300 words, so you can click the paragraphs you'd want to add from the output or click the small paste button on the top right corner of the output to paste all of its content into your document.
There's also a "load more" button at the bottom of the output to load another one to find potential text for your document.