Your attempts did not work because the index page is not a normal wiki page.
You can do what you want via redirect rules in the
.htaccess file. But of course for that you need advanced knowledge and experience.
A simpler way is to place a menu tree on the start page via a navigation plugin. These typically have similar or the same functions as the index/sitemap display. In addition, they offer many adjustment options.
Take a look at the
plugins with the tag "navigation"
Feedback welcome - Michael Sy.