In Mendix, the root URL (/) is designed to always serve the Mendix index.html file. There is no built-in setting that lets you tell the runtime to serve arbitrary raw HTML as the homepage instead.
What you can do is override the default file by placing your own index.html inside the theme/web/ folder. In that case, your HTML page will load at the root URL. However, this also means the Mendix client will not start there anymore. You are effectively serving only your static page instead of the Mendix app UI.
This works locally.
But, sadly, the build on the Mendix Cloud fails when you do this.
[compile] 2026-02-11T00:15:03.663323750Z ERROR at (unknown location): theme/web/index.html does not contain the expected elements for the React client. This can happen when switching between the Dojo and React client without updating the template, or when manually editing the template. [compile] 2026-02-11T00:15:03.665590222Z BUILD FAILED
You can follow this document. Also, if there are any parts that belong to Dojo or are deprecated, you need to remove them.