P.S. I know it’s a bad practice to use multiline cells, but that’s the only option available to me)
In column B:
=REGEX(A1;"\n \n";"";"g") to supress lines without text (there is a space in every line)
In column C:
=REGEX(B1;": \R ";": ";"g") to join in a line Concept: and Value
Then copy column C, and paste as Text and Numbers.
LibreOffice Help on REGEX.
More info on Regular Expressions.
Edit your question if you want to add more information; also can comment an answer. Do not use Add Answer to comment.
Check the mark () to the left of the answer that solves your question.
Thank you very much!