This is an example of how you can build Next.js, or any other Javascript front-end framework into assets that you can use in your Rust API back-end. This example currently only holds one page, but you can easily extend this using the default page methods (in Next, this would be just adding another file/folder to the "pages" folder as appropriate).
This particular example was built for a Hashnode article about how you can use Javascript front-end frameworks with Rust. As you can see, it's quite barebones but as you can basically extend this example in any way that you want, as long as the front end assets compile it should be quite simple to do so.