While running Pipelines, there is an error that says "Validation error: This pipe requires a single item target, not a list"

It sounds like you are looking for a record and although you may have unique records and only 1 response, Quickbase returns the record as an array. So even if it's 1 result, it sees it as many (Because it doesn't know for a fact this will always be true)

To handle this, just add a For Each loop before the update.
Reach out if you would like some help