“Extract Annotations” was a feature of the third-party ZotFile extension. In Zotero 6, that feature has been replaced by Zotero's own advanced PDF functionality.

You can create a note from all of an item's annotations by right-clicking an item in the items list and selecting “Add Note from Annotations”, or you can open the PDF in the new built-in PDF reader and add annotations selectively. See Adding Annotations to Notes for more on the various ways of using annotations in notes in Zotero 6

For more details on the new functionality, see the Zotero 6 announcement.