How to use computed setter with Typescript?

I’ve scoured the internet and can’t seem to find anyone talking about this, so I’m either doing something wrong or just can’t figure out how to search for the answer.

Basically, I’m using Typescript in a Vue 3 project (actually Nuxt 3, but I don’t think that matters here) and I want to use a getter/setter in one of my computed values. However, when I try to set the value, Typescript complains that I’m trying to set the value of a read-only property (which is normally true for ComputedRef, but mine has a set method). How am I supposed to do this?

In the setup for an off-canvas menu component:

 <script setup lang="ts">
  const store = useStore()
  const route = useRoute()

  const isShowing = computed(() => ({
    get(): boolean {
      return store.showOffcanvasMenu
    },
    set(value: boolean) {
      store.setShowOffcanvasMenu(value)
    }
  }))

  watch(() => route.fullPath, () => {
    isShowing.value = false // Typescript doesn't like this!
  })
</script>

When I try to set isShowing.value = false, Typescript complains with this error: "Cannot assign to ‘value’ because it is a read-only property.". What’s the correct way to utilize the computed ref’s setter?