What harmonization method is a cross-channel entity available in all data streams?

The correct answer is Custom Classification, which serves as a harmonization method that facilitates the alignment and organization of data across different channels within Marketing Cloud Intelligence. Custom Classification allows users to define and categorize data points according to their specific business needs, ensuring that similar types of data are grouped together across various data streams. This method is particularly beneficial when there are disparate data formats or standards across channels, as it enables a consistent approach to data representation.

This customization ensures that adverse differences in data schema do not hinder analysis, offering a versatile solution across all data streams. Furthermore, it empowers marketers to evaluate and compare performance metrics from different channels effectively, offering meaningful insights that are tailored to the organization's specific requirements. This capability makes Custom Classification a robust tool for managing cross-channel data harmonization.