Updated

assets/my-component.js

@@ -2,3 +2,13 @@ Vue.component('my-component', {
   template: '<div>Hello from My Component!</div>',
   // Add your component's data, methods, etc. here
 });
+
+const app2 = Vue.createApp({
+  data() {
+    return {
+      message: 'Hello World!',
+    };
+  },
+});
+
+app.mount('#app2');

sections/header.liquid

@@ -139,15 +139,7 @@
       });
   });
 
-  const app2 = Vue.createApp({
-    data() {
-     return {
-      message: "Hello World!"
-     }
-    }
-   })
-   
-   app.mount('#app2');
+  
 </script>
 
   <header class="header header--{{ section.settings.logo_position }} header--mobile-{{ section.settings.mobile_logo_position }} page-width{% if section.settings.menu_type_desktop == 'drawer' %} drawer-menu{% endif %}{% if section.settings.menu != blank %} header--has-menu{% endif %}{% if has_app_block %} header--has-app{% endif %}{% if social_links %} header--has-social{% endif %}{% if shop.customer_accounts_enabled %} header--has-account{% endif %}{% if localization_forms %} header--has-localizations{% endif %}">