When you position the notes at end of document, the Start at menu is disabled to avoid a number ambiguity. Writer uses a single sequence counter which cannot be customised to prefix it with the chapter number. Therefore, a note number which would be reset at the start of every chapter would be ambiguous, even with the trick of repeating the chapter heading in the notes as done in 70590/grouping-endnotes-by-chapter.
Since your requirement is to group (number) notes by chapter, would it be acceptable for you to position your chapter notes at end of every chapter?
If so, make your chapters a section:
- select chapter heading and its content
Footnotes/Endnotes tab, check Collect at end of text and Restart numbering
Repeat for each chapter.
Setting can be different for footnotes and endnotes (thus keeping “global” notes at end of document rather than at each chapter).
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