Using

  export const dynamic = "force-dynamic";
  export const fetchCache = "force-no-store";

sitemap.ts

import { MetadataRoute } from "next/types";

export const dynamic = "force-dynamic";
export const fetchCache = "force-no-store";

const { APP_URL } = process.env as any;

export async function generateSitemaps() {
  return [{ id: 1 }, { id: 2 }, { id: 3 }, { id: 4 }, { id: 5 }];
}

export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
  // fetch for data
  const res = await generateSitemaps();

  return res.map((data: any) => {
    const content = data.content || {};

    return {
      url: `${APP_URL}/${content.id}`,
      lastModified: `${
        new Date(new Date().setMonth(new Date().getMonth() - 2))
          .toISOString()
          .split("T")[0]
      }T08:00:00+08:00`,
      changeFrequency: "monthly",
      priority: 0.9,
    };
  });
}

Logs

Generating static pages (0/20)  [    ]
Error occurred prerendering page "/sitemap/1.xml". Read more: https://nextjs.org/docs/messages/prerender-error

Error: Invariant: `dynamic-error` during static generation not expected for app routes. This is a bug in Next.js