In short: no. At their heart, Mendix apps are web applications that use HTML and JS on the front end, and then a web server and database on the back-end.
There are ways to use custom HTML and custom JS in a Mendix app by using the HTMLSnippet widget in the app store or by creating custom widget, but probably not in the way you’re thinking.
The question about exporting a Mendix project to an HTML project doesn’t make much sense. because again at their heart, the Mendix app is already HTML and JS.
If you have a specific question about implementing or recreating certain functionality in Mendix, feel free to post another question.