I replied in some other thread. Copy-pasta:

No, your personal data is not sold or rented or given away or bartered to parties that are not Plaid, your bank, or the connected app. We talk about all of this in our privacy policy, including ways that data could be used — for example, with data processors/service providers (like AWS which hosts our services) for the purposes of running Plaid’s services or for a user’s connected app to provide their services.