fix(runtime-core): stricter compat root mount check

packages/runtime-core/src/compat/global.ts

@@ -472,6 +472,7 @@ function installCompatMount(
     }
     setupComponent(instance)
     vnode.component = instance
+    vnode.isCompatRoot = true
 
     // $mount & $destroy
     // these are defined on ctx and picked up by the $mount/$destroy

packages/runtime-core/src/renderer.ts

@@ -1301,7 +1301,8 @@ function baseCreateRenderer(
   ) => {
     // 2.x compat may pre-creaate the component instance before actually
     // mounting
-    const compatMountInstance = __COMPAT__ && initialVNode.component
+    const compatMountInstance =
+      __COMPAT__ && initialVNode.isCompatRoot && initialVNode.component
     const instance: ComponentInternalInstance =
       compatMountInstance ||
       (initialVNode.component = createComponentInstance(

packages/runtime-core/src/vnode.ts

@@ -136,6 +136,11 @@ export interface VNode<
    */
   [ReactiveFlags.SKIP]: true
 
+  /**
+   * @internal __COMPAT__ only
+   */
+  isCompatRoot?: true
+
   type: VNodeTypes
   props: (VNodeProps & ExtraProps) | null
   key: string | number | null