This book that I'm preparing for reprinting has two kinds of endnotes, one set goes at the end of each chapter and another is collected in an appendix. I'm not sure how to handle that second set in LibreOffice. There seem to be some third party extensions, but I don't think this is their purpose. They are intended to help researchers in handling citations and bibliographies. They do seem interesting in themselves though. The one that I downloaded is called Zotero, and it is in the Debian repositories. I could imagine that this could be a powerful tool for writers and researchers.
But I'm still stuck with this problem of the endnotes. 🙁