Footnotes in Writer are automatically inserted as new lines in the footnotes area, which may look like this:
---
______
1. text of footnote nr1
2. text of another seconde footnote
3. text of still another one
4. etc you get the idea.
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This can be quite inconvenient when using short footnotes because wastes a lot of space. It would be much more efficient use of space if one could set footnotes like this:
---
______
1. text of footnote nr1 [separator]2. text of another seconde footnote [separator]3. text of still another one [separator]4. etc you get the idea.
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[separator] could be user-defined, for example comma, semicolon, tab, space, custom character, etc.

There is a post which nicely explains this, unresolved for many years:https://ask.libreoffice.org/en/question/58631/footnotes-continuing-on-the-same-line/