Hello!
"Extract Annotations" has been a feature offered by third-party ZotFile as a free plugin, and useful along with Zotero.
In recent Zotero 6, that feature has been updated and replaced by Zotero's own advanced PDF feature.
You can easily add annotations to notes right from the PDF reader by right-clicking an item in the items list and selecting "Add annotations to notes", or open the PDF in the new built-in PDF reader and add annotations.
Please refer to the Zotero 6 announcement for more details on the new functionality and Adding Annotations to Notes for more details on using annotations in notes in Zotero 6.