How to automatically create a topic list in a sub-category?

An alternative approach:

Why don’t you put all of the Topics into their own Sub Category and share the link to the Sub Category, which will bring up a Topic List containing all of your Topics?

Then there is no need to create an ‘index’ Topic? The Topic List for the Sub-category IS your index?

Here’s an example here on Meta:

https://meta.discourse.org/c/plugin/extras/5

which will take you to:

which is a Topic List.

Like any Topic List it contains viewing stats.

Another useful alternative (if you can’t put them all in one sub-category and they are spread around) is to use tags.

Add a tag to each Topic and then link your users to that tag list, e.g.:

https://meta.discourse.org/tag/official

https://meta.discourse.org/tag/official

All of the topics here have tag ‘offiical’.

Again, it’s a Topic List with viewing stats …