Sitemap is not executed. Its used by bots. If you are dynamically generating it, its available on both development and build.

Refer to:
https://nextjs.org/docs/app/api-reference/file-conventions/metadata/sitemap#generating-multiple-sitemaps

If you read that documentation you can also figure out however you want to use the slug.

Yeah generated* sorry

I copied the code from the doc and adapted it by changing the id to a string but it doesn't work, I get a 404

https://nextjs.org/docs/app/api-reference/file-conventions/metadata/sitemap#generating-multiple-sitemaps

import { MetadataRoute } from 'next';

export async function generateSitemaps() {
  return [{ user: 'john-doe' }];
}

export default async function sitemap({ user }: { user: string }): Promise<MetadataRoute.Sitemap> {
  const products = ['john-doe'];
  return products.map(product => ({
    url: `localhost:3000/users/${user}`,
    lastModified: new Date(),
  }));
}

Did you account for this?

Yup

Tried to access this http://localhost:3000/sitemap.xml/john-doe

Up