Remove a horizontal line in LibreOffice
If you type several hyphens in a row and then return - you get a horizontal line.
With every further return on the line, new lines are added, and the one original line can no longer be deleted using the keyboard.
The line is a paragraph formatting.
To get this line deleted you have to go through the menu:
> Format> Paragraph> "Border" tab
Under the item "Line arrangement" click on the box without a border.