Welcome to the community, @Arturo_Sanchez_Corre! :grinning_face_with_big_eyes: I’m not aware of a way to do what you want. The way that any Airtable block interprets the data coming from a field is determined by whoever wrote that block. The data type can’t be overridden anywhere.
To put a more fine point on it, what you want isn’t necessarily for a lookup to act like a multiple select. What you want is the same type of data that a multiple select delivers, which is an array. In some cases, a lookup will deliver an array; other times, including this one, it delivers a string.
That aside, you might consider using a rollup field instead, with an aggregation formula that just reads “values”, meaning that the data is left as an array, and that array might be delivered intact to the pivot table block.
There’s an ever-so-slight difference in the way that lookup and rollup fields collect data and present them elsewhere. I’m doing a deep dive into the two to compare them, and will be sharing my results once I’m done. In the meantime, try changing your source field from lookup to rollup and see if it makes a difference. It’s worth a shot, at least. While I might not always get the results I want from a test, testing always teaches me something that I can use down the road.
