I don't know if that was the right solution, however it worked for me 🙂 @virk
1) I installed manually a theme named Argon-alt Template using the Extension Manager since I couldn't install it using the Search and Install function.
2) I read the theme's description and found a section named Sidebar which had the following content "Sidebar works with bullet points, linebreaks, and headers. "
3) I went to Configuration Settings > Basic > sidebar
and entered wiki:sidebar
on the textbox next to it.
4) Typed https://www.<your-domain>.com/doku.php?id=wiki:sidebar
on my browser's navigation bar.
5) Finally I created and entered some values to the page of wiki:sidebar which was empty.
Example:
=== First section ===
* [[news:2017_01_06|News I 2017]]
* [[news:2017_01_06|News II 2017]]
=== Second section ===
* [[news:2017_01_06|News I 2017]]
* [[news:2017_01_06|News II 2017]]
Preview of the result: https://imgur.com/xVjKmmZ