How to create a new field with the footnote number

LibreOffice 7.3.7.2 on Linux _ Insert _ Field _ More Fields _ Document _ Footnote (is still missing here)
How can I add the Footnote (number) in the menu
LibreOffice _ Insert _ Field _ More Fields _ Document _ Footnote
?
Application case: Text document with more than 10 footnotes. One of the footnotes (number 7) is identical with one footnote (number 5) already existing. The second mentioning in footnote 7 can be for example:
“7 see footnote 5”
“5” could be a field, but I see no possibility to define such a footnote field.
Maybe the solution exists already in libreoffice (crossreference ?, …?). I have no knowledge about crossreference and many other libreOffice functions and possibilities. If you know a better libreOffice menu item, please give me this hint.

What do you mean? There is no Footnote entry in Document tab.
Do you want to insert a cross-reference to an existing footnote? Explain your use case.

I have updated my question. See above.

Solution B is best for me. It is closest to the Oxford University Standard for the Citation of Legal Authorities Fourth Edition 2012 which I am using.
Solution A works in *.odt files, but not in *.doc and *.docx (inside LibreOffice). In *.doc their is no jump to the first footnote (cross-referenced footnote) when clicking on the footnote. I used for the last step in solution A on LibreOffice 7.2:
Mark Cross-reference _ Ctrl Shift P (Superscript Icon in top menu bar)
or
Mark Cross-reference _ Format _ Character _ Position _ Superscript.
Maybe, I did not understand the last step correctly. Please correct me if I misunderstood the last step.

DOC and DOCX are different standards from ODF. Writer (abiding by the OASIS standards) has a more systematic and methodic approach to formatting and layout (you can read “it is better specified”) and provides many primitives not present in DOC(X), notably character, page, frame and list styles.

In addition, DOCX specification is not publicly available. Most of its encoding had to be guessed by retro-engineering. But, anyway, many features cannot be translated exactly because the needed primitive does not exist in the other standard. Consequently, you get an approximate encoding which cumulatively damages your document if you have too many editing sessions with saving in an non-native format. This is why you should always work in native format until your document is finalised. Only then, you can export (only once) in an alien format but translation will never be 100% correct.

If by “last step” you mean formatting the cross-ref so that it looks like a usual footnote anchor, this formatting has no effect on hyperlinks (the feature used to jump to various destinations). Using toolbar button or Format>Character is called direct formatting and will make your life more difficult than using character styles. However, if you save DOC(X), you can’t do anything else because there is no character styles in this format. And saving DOC(X) surely has an impact on hyperlinks. It depends on the encoding, both at source and destination locations.

My best advice is to recommend to work .odt exclusively. Note however that converting an already edited .docx to .odt does not eliminate the existing approximated conversions and DOCX multiple idiosyncrasies and this will play nasty tricks. The only safe way is to paste your discourse as unformatted text in a new document and to restyle/reformat everything.

DOCX was probably imposed upon you. Word claims it can read (and produce) .odt document. So, you can send an .odt and put the blame on Word misinterpreting your document (because first thing M$ did was to implement a non-endorsed modified version of ODF so that its captive market wwas kept locked).

You have two possibilities when footnotes are identical. Both are based on cross-references and equally “complex”.

A. Don’t create a new footnote, reference an existing one.

Where you’d have inserted your new footnote #7 (with Insert>Footnote & Endnote>Footnote, instead Insert>Cross-reference. The cross-reference dialog opens in Cross-references tab.

  1. in Type select Footnotes
  2. in Selection click on the target existing note
  3. in Refer using, make sure Referenced text is selected (to get the note number)
  4. Insert

The note number is inserted in your text as an “ordinary” character. To make it look like a note anchor, select it and apply character style Footnote Anchor.

B. Make an indirection in a dedicated note

Create you footnote #7. Type text "*See footnote " then Insert>Cross-reference. Follow the same steps as above. The footnote anchor is inserted as “ordinary” text but does not need to be formatted differently from the rest of the note.

Sample file: AskLONoteXref.odt (33.3 KB) where I used both techniques. There are three occurrences of word “dolor”. The first one holds the original note. The second one is a cross-reference to the previous note. The thirs one has an “indirect note” where the xref is in the note.