I think the confusion and difficulty might be that the Index Topic has to be in a certain format, and this is not completely clearly stated in the documentation (top post)
I had installed this plugin myself, carefully following the instructions, but it wasn’t working in exactly the same way @dennisjbr was experiencing.
It might help to have an example of the Markdown required rather than linking to the Meta example, because the only key rule is that there MUST be a Markdown bulleted/numbered list. The docs say ‘a list’ but the word ‘list’ has an ordinary English usage which includes non-Markdown lists!
This will work as an Index Topic:
* https://meta.discourse.org/t/discourse-doc-categories/322376
* Some Arbitrary Text: https://meta.discourse.org/t/discourse-doc-categories/322376
This will not work:
https://meta.discourse.org/t/discourse-doc-categories/322376
Some Arbitrary Text: https://meta.discourse.org/t/discourse-doc-categories/322376
Beyond this you can use Markdown headings to create sections and use multiple lists, but nothing will appear in the sidebar unless there’s a Markdown list. I appreciate this is a bit obvious and may not have tripped up anyone else, but it did catch me out (stupidly or not) and I’m not new to Discourse, TCs and Plugins.