HTML file in folder: not found

Im having the same problem , Normal Html file. Popped it into a folder and not found

The bug causing the issue in the topic that you replied to has been solved.
Move the files out of the folders. Having index.html in the html folder, for example, means that it is served at the route /html.
You could also move only the HTML out, but then you would have to update the references to the CSS and JS, for example /Main.css/css/Main.css.