VueJS Router - How do I stop multiple active routes when using sub routes and Vuetify?

You have to add exact (or exact={true}) prop to <v-list-item> component:

<v-list-item
  v-for="item in items"
  :key="item.title"
  :to="item.route"
  exact

></v-list-item>

On v-list-item docs for exact:

Exactly match the link. Without this, '/' will match every route. You can find more information about the exact prop on the vue-router documentation.

You can check that out:

https://vuetifyjs.com/en/components/list-item-groups#list-item-groups