It's a pity that there is less discussion in this Forum on how to actually use Zotero for different writing needs, than there is on how to fix problems. That link is the sort of discussion for which it has been suggested that this Forum needs different sub-forums, to encourage discussion of such topics.

With such a discussion, I am sure there would be alternative options to those proposed in that link, that people use to create an annotated bibliography early in scoping out a writing task (where final formatting is not that important). The suggested approach appears to have been written prior to the advent of the Zotero PDF viewer in v6. So there are now additional approaches available. But even prior to that, there were/are approaches that don't involve the suggested need to replace each item's abstract with your summary, placing large chunks of directly quoted text in the Extra field, and then using a custom Style to get all that out.

For example, off the top of my head, one could add a child note to each item and add your summary of the item to that, while reading the PDF in the Zotero viewer. Then select all the items in the sub-collection and use Generate Report From Items to put all the summaries in a single report (that can be printed to PDF and then added to the collection, or saved as a single HTML file, or copy/pasted into a standalone note at the top of the sub-collection, or copy/pasted to a word processor document for further editing). If you would prefer that each reference be correctly styled in its summary/child note, you could instead just paste the result of Generate Bibliography from Item into its child note. You can also get the annotations you added to the item's PDF sent to a child note (where they can be edited).

Your master annotated bibliography could then be created by combining the overall summaries from each sub-collection.

I am sure that there are even more powerful/complex ways of doing this, that exploit things like tagged annotations, external apps like Obsidian etc. But as a novice user I would start with something relatively straightforward like the above.