No way to create index page for page-folders [Not working for folders - 2020]

This is not true, you are quoting a very old post from 2016

I’ve since renamed both the index page and CMS collection to projects.

The index page method still can be achieved

I still have both an index page at /projects and individual CMS items starting with /projects/{slug}

Here are the new URLs since you mentioned them:

Samuel Liew - Projects (page without any folder, with slug “projects”)
Tic-Tac-Toe by samliew (page inside a folder “projects”)
Set Game by samliew (page inside a folder “projects”)

Screenshot in Webflow Designer

Screenshot_2024-01-26_170106