Pages url not pulling index.html

I’m getting the 404 site not found error on my page “https://ian6ft5.github(dot)io” but if I type in “https://ian6ft5.github(dot)io/index.html” it goes to the homepage and functions as intended. In the top folder of the repository there is only the single index.html file and folders containing the content & stylesheet. I do not have a README.md but as I understand github pages is supposed to look for index.html, index.md, README.md in that order, so it seems that lack shouldn’t be an issue. The repository contains no submodules, just text files, images, and folders

On a whim I decided to add a README.md file to the repository and now it works when I go to the main URL. So it’s fixed, but if anyone wants to comment with an explanation of why that would cause an issue I’d be very glad to hear it.

this is the root:
https://ian6ft5.github.io/

this is with the index.html and it is the same thing,
https://ian6ft5.github.io/index.html

your only error is that you need to include .io to complete the URL, remember it is [yourusername].github.io