Simple way to know if loading vs not found in Vue:

const item = useObservable(Dexie.liveQuery(() => db.items.get(id.value).then(o => o || null)))

// Handle not found (undefined = still loading, null = not found)
watch(item, (newItem) => {
  if (newItem === null) {
    // HANDLE NOT FOUND
  }
})