Can Data Views be queried in DESelect Segment?

yes, all the data views (23) that are available in sfmc can be used in deselect segment as well they can be found under available data extensions and are available to query from (just like you would work with a data extension) they can be distinguished from data extensions easily since they all start with an underscore for example, you can get the first and last names of all contacts in a data extension that are already subscribers in salesforce marketing cloud a step by step guide on how to use data view ( subscribers) in deselect segment can be found https //support deselect com/hc/en us/articles/360003127678 select contacts that are known subscribers