what.js

function update(cache, payload) {
    cache.evict(cache.identify(payload.data.deleteCartItem));
  }

  const [removeFromCart, { loading }] = useMutation(REMOVE_FROM_CART_MUTATION, {
    variables: { id },
    update,
    // When the optimistic response comes back, it seems to re-fetch every single query on the page, leaving `data` from queries undefined (and loading and error undefined as well), causing the layout to break.
//  // The error itself comes from next.js, and it does seem that the item is evicted from the cache before that happens...
    // optimisticResponse: {
    //   deleteCartItem: {
    //     __typename: 'CartItem',
    //     id,
    //   },
    // },
  });

Hi, they fixed that bug in modern versions of @apollo/client (I am using 3.6.9), update it and it will work
or you can wrap evict inside setTimeout, like this:

setTimeout(() => { cache.evict(cache.identify(payload.data.deleteCartItem)); }, 0);

and it also will work with OptimisticResponse.