Can I Sync Salesforce Unified Objects Using Fivetran?

No, it's not possible to sync unified objects, such as UnifiedActivity, using Fivetran. Unified objects are available only for reporting purposes in Salesforce and aren't accessible using Salesforce Object Query Language (SOQL) or the Salesforce API. As a result, we can't obtain or sync the relevant object data. For more information, see our Unsupported Salesforce object types documentation.

Salesforce documents this limitation in each unified object's reference documentation. For more information, see Salesforce's Standard Objects API documentation.