Try revalidateTag

src/app/posts/[slug]/page.tsx

@@ -18,10 +18,7 @@ export async function generateMetadata({
       title: frontmatter.title,
       description: excerpt,
       openGraph: {
-        title: {
-          default: siteMetadata.title,
-          template: `%s | ${siteMetadata.title}`,
-        },
+        title: frontmatter.title,
         description: excerpt,
         url: `${siteMetadata.origin}/posts/${slug}`,
         siteName: siteMetadata.title,

src/app/rss.xml/route.ts

@@ -1,8 +1,9 @@
 import RSS from 'rss';
+import { revalidateTag } from 'next/cache';
 import { getPosts } from '@/internals/posts';
 import siteMetadata from '@/siteMetadata';
 
-export const revalidate = false; // Cache forever like a static file
+// export const revalidate = 0; // Cache forever like a static file
 
 export async function GET() {
   const feed = new RSS({
@@ -16,11 +17,24 @@ export async function GET() {
 
   for (const post of posts) {
     const postUrl = new URL(`/posts/${post.slug}`, siteMetadata.origin).href;
-    const html = await fetch(postUrl, { redirect: 'follow' }).then((res) =>
-      res.text(),
+    const html = await fetch(postUrl, {
+      next: { tags: ['rss'] },
+    }).then((response) => response.text());
+    const isBuilding = !html.includes(
+      `<meta property="og:site_name" content="${siteMetadata.title}"/>`,
     );
-    const contentHtml =
-      html.match(/<main(?:[^>]*?)>([\s\S]+?)<\/main>/)?.[1] || '';
+
+    if (isBuilding) {
+      revalidateTag('rss');
+      return new Response('Site building..., please try again later.', {
+        status: 503,
+        headers: {
+          'Retry-After': '60',
+        },
+      });
+    }
+
+    const contentHtml = html.match(/<main(?:[^>]*?)>([\s\S]+?)<\/main>/)?.[1];
     const image = html.match(
       /<meta property="og:image" content="([\s\S]+?)"\s?\/?>/,
     )?.[1];