Try a local absolute path for the OG image, to see what happens

src/lib/blocks/Post.svelte

@@ -4,6 +4,7 @@
   import { metadata } from "$lib/store";
   import { title as siteTitle, ogSlug, blogSlug, ogImageBlog } from "$lib/config";
   import { formattedPubDate, fetchAuthorMetadata } from "$lib/utils";
+  import { base } from '$app/paths';
 
   import Metadata from "$lib/components/Metadata.svelte";
 
@@ -22,7 +23,7 @@
 
   let authorMetadata = { src: "", name: "" };
   const slug = $page.url.pathname.replace(`/${blogSlug}`, '').replaceAll('/', '');
-  const customOgImagePath = `${$page.url.origin}/assets/${ogSlug}/${slug}.png`;
+  const customOgImagePath = `${base}/assets/${ogSlug}/${slug}.png`;
 
   onMount(async () => {
     authorMetadata = await fetchAuthorMetadata(author);
@@ -36,6 +37,12 @@
     url: $page.url.href,
     image: customOgImagePath || ogImageBlog,
   });
+
+  // Debugging, remove later
+  console.log('Base:', base);
+  console.log('Slug:', slug);
+  console.log('Custom OG Image Path:', customOgImagePath);
+  console.log('Page URL:', $page.url.href);
 </script>
 
 <Metadata prism={true}/>

svelte.config.js

@@ -65,11 +65,9 @@ const config = {
       handleMissingId: "warn",
       entries: ["*"],
     },
-    /*
     paths: {
-      base: process.env.NODE_ENV === "production" ? "/sveltekit-gh-pages" : "",
+      base: process.env.NODE_ENV === "production" ? "" : "",
     },
-    */
   },
   extensions: [".svelte", ".md"],
   preprocess: [mdsvex(mdsvexOptions), vitePreprocess()],

vite.config.js

@@ -5,6 +5,11 @@ import copyImages from "./scripts/vite-plugin-copy-images";
 /** @type {import('vite').UserConfig} */
 export default defineConfig({
   plugins: [sveltekit(), copyImages()],
+  server: {
+    fs: {
+      allow: ['static']
+    }
+  },
   build: {
     sourcemap: false,
   },