fix(VTreeview): wrong isOpen state in prepend slot

fixes #20830

Author: yuwu9145

packages/vuetify/src/composables/nested/nested.ts

@@ -130,7 +130,7 @@ export const useNested = (props: NestedProps) => {
   const children = ref(new Map<unknown, unknown[]>())
   const parents = ref(new Map<unknown, unknown>())
 
-  const opened = useProxiedModel(props, 'opened', props.opened, v => new Set(v), v => [...v.values()])
+  const opened = useProxiedModel(props, 'opened', props.opened, v => new Set(toRaw(v)), v => [...v.values()])
 
   const activeStrategy = computed(() => {
     if (typeof props.activeStrategy === 'object') return props.activeStrategy

packages/vuetify/src/composables/nested/openStrategies.ts

@@ -1,3 +1,6 @@
+// Utilities
+import { toRaw } from 'vue'
+
 export type OpenStrategyFn = (data: {
   id: unknown
   value: boolean
@@ -47,12 +50,12 @@ export const singleOpenStrategy: OpenStrategy = {
 export const multipleOpenStrategy: OpenStrategy = {
   open: ({ id, value, opened, parents }) => {
     if (value) {
-      let parent = parents.get(id)
+      let parent = toRaw(parents.get(id))
       opened.add(id)
 
       while (parent != null && parent !== id) {
         opened.add(parent)
-        parent = parents.get(parent)
+        parent = toRaw(parents.get(parent))
       }
 
       return opened

packages/vuetify/src/labs/VTreeview/VTreeviewChildren.tsx

@@ -128,7 +128,7 @@ export const VTreeviewChildren = genericComponent<new <T extends InternalListIte
       return children ? (
         <VTreeviewGroup
           { ...treeviewGroupProps }
-          value={ props.returnObject ? item.raw : treeviewGroupProps?.value }
+          value={ props.returnObject ? toRaw(item.raw) : treeviewGroupProps?.value }
         >
           {{
             activator: ({ props: activatorProps }) => {