Explanation: The Salesforce field type that is unsupported for syncing with Marketing Cloud Account Engagement is Lookup. Lookup fields are fields that allow you to create a relationship between two objects in Salesforce, such as Account and Contact. Marketing Cloud Account Engagement does not support syncing Lookup fields, because they are not compatible with Marketing Cloud Account Engagement’s data model and could cause data inconsistencies or errors. Marketing Cloud Account Engagement supports syncing most other Salesforce field types, such as Text, Number, Picklist, and Formula.