use extends

__tests__/e2e/.vitepress/theme/index.ts

@@ -3,7 +3,7 @@ import DefaultTheme from 'vitepress/theme'
 import CustomAppearance from './CustomAppearance.vue'
 
 export default {
-  ...DefaultTheme,
+  extends: DefaultTheme,
   enhanceApp({ app }) {
     app.component('CustomAppearance', CustomAppearance)
   }

docs/en/reference/default-theme-nav.md

@@ -192,14 +192,17 @@ Then, you need to register the component globally:
 
 ```js
 // .vitepress/theme/index.js
-import AnotherCustomComponent from './components/AnotherCustomComponent.vue'
+import DefaultTheme from 'vitepress/theme'
+
 import MyCustomComponent from './components/MyCustomComponent.vue'
+import AnotherCustomComponent from './components/AnotherCustomComponent.vue'
 
 /** @type {import('vitepress').Theme} */
 export default {
+  extends: DefaultTheme,
   enhanceApp({ app }) {
-    app.component('AnotherCustomComponent', AnotherCustomComponent)
     app.component('MyCustomComponent', MyCustomComponent)
+    app.component('AnotherCustomComponent', AnotherCustomComponent)
   }
 }
 ```