I would not blame you for dumping Libre Office for this most annoying problem.
Instead of providing a solution, the advice here has been to submit to default “styles” that might suit a potential reader, (as well as solutions that simply do not work, which are not helpful).
If you are still about, (and, for those who might seek a solution, here, later), this is my suggestion:
Go to the head (top) of your text document).
Select “Styles.”
Under “Styles,” select “Edit Styles.”
In the box that appears, select the tab marked “Indents & Spacing.”
At “Line Spacing,” select “Single.”
Check the box below this to “Activate page line-spacing.”
Watch out that Libre Office may re-adjust the “Spacing” above to add space between paragraphs; so, if it does this, (automatically, just to frustrate your efforts), set these settings back to “0.00” above and below the paragraphs.
Click “Apply,” and see that your new settings for this text document show “Line Spacing” as “Single,” with a check in “Activate page line-spacing,” and, the settings for “Spacing” are “0.00” above and below the paragraphs.
Select “Okay.”
That should change your text document back to something more like a typewriter, (if you just want a simple blank line to separate your paragraphs or lines of text, without adding some extra space and without changing other formatted items, such as italicized text).
