Github: page not found for post but opens for index.html

I'm creating a personal website for myself so I have my directory uploaded to github. The website is linked to githubusername.github.io and it works fine for me when I open it up but when I click on a post on that website, I get a "404 File not found" error from github.

The post has a link tag to minesweeper.html located in index.html.

<a href="minesweeper.html"><img src="assets/img/Minesweeperimg.png" alt="" class="img-fluid">

Here's a picture of my file structure.1

Why am I getting the error and how do I fix it? When I run the html locally, it runs fine.