Try lib helper ts file agian...

src/lib/utils/SlugFromPath.ts

@@ -0,0 +1,2 @@
+export const slugFromPath = (path: string) =>
+	path.match(/([\w-]+)\.(svelte\.md|md|svx)/i)?.[1] ?? null;

src/routes/blog/[slug]/+page.server.ts

@@ -0,0 +1,20 @@
+import type { EntryGenerator } from './$types';
+import { slugFromPath } from '$lib/utils/SlugFromPath';
+
+// https://kit.svelte.dev/docs/page-options#prerender-troubleshooting
+export const entries: EntryGenerator = async () => {
+	const modules = import.meta.glob(`/src/blogs/*.{md,svx,svelte.md}`);
+	const postPromises = Object.entries(modules).map(([path, resolver]) =>
+		resolver().then(
+			(post) =>
+				({
+					slug: slugFromPath(path),
+					...(post as unknown as App.MdsvexFile).metadata
+				}) as App.BlogPost
+		)
+	);
+
+	const posts = await Promise.all(postPromises);
+	return posts;
+};
+export const prerender = true;