optimistic updates tRPC v11 + TanStack Query v5

I am reading https://tanstack.com/query/latest/docs/framework/react/guides/optimistic-updates#if-the-mutation-and-the-query-dont-live-in-the-same-component and I am a bit confused on the best way to implement the optimistic updates 'Via the UI'. How would I access variables from useMutationState?
Optimistic Updates | TanStack Query Docs
React Query provides two ways to optimistically update your UI before a mutation has completed. You can either use the onMutate option to update your cache directly, or leverage the returned variables to update your UI from the useMutation result. Via the UI
I am just using the cache approach for now

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