TypeScript issue when using Promise.allSettled

Conditional chaining doesn't change the fact that, from a type perspective, you're trying to use a property that isn't there. It just defends against your proceeding if the property contains the value undefined. You're still trying to use a property that may not exist on the type.

You can use a type guard to filter out the failed responses. For instance, an inline type guard:

const neuroResponses = await Promise.allSettled(neuroRequests);
const ret = neuroResponses
    .filter(response => "value" in response && response.value.data?.result[0]?.generated_text?.length > 0)
    .map(({ value }) => value.data.result[0]?.generated_text);

If you do this a lot, you might want a type guard function:

function isSuccessful<T>(response: PromiseSettledResult<T>): response is PromiseFulfilledResult<T> {
    return "value" in response;
}

Then you can use it like this:

const neuroResponses = await Promise.allSettled(neuroRequests);
const ret = neuroResponses
    .filter(isSuccessful) // ***
    .filter(response => response.value.data?.result[0]?.generated_text?.length > 0)
    .map(({ value }) => value.data.result[0]?.generated_text);

Or

const neuroResponses = await Promise.allSettled(neuroRequests);
const ret = neuroResponses
    .filter(response => isSuccessful(response) && response.value.data?.result[0]?.generated_text?.length > 0)
    .map(({ value }) => value.data.result[0]?.generated_text);