In Vuetify 2.6 I use this.

/* close animation v-tab */
.v-window-x-transition-enter-active,
.v-window-x-transition-leave-active,
.v-window-x-reverse-transition-enter-active,
.v-window-x-reverse-transition-leave-active {
  transform: none !important;
  transition: none !important;
}