In Custom CDS Views app, when you try to add a filter, the associated data source(s) with cardinality [0..*] or [1..*] are not visible.
SAP S/4HANA CLOUD
Reproducing the Issue
1. Open a custom CDS view in app Custom CDS Views
2. Go to Filter tab, Edit and then try to add a filter
3. In the 'Select: Field for Filter' pop-up, the associated datasource with cardinality [0..*] or [1..*] does not show up
When [0..*] or [1..*] is used in Association, a field of the associated view (or table) cannot be used in WHERE condition and cannot be added using Extend View either.
Read more explanation in blog: Cardinality of Association in CDS View | SAP Blogs
This is an expected behavior as explained above.
associated data source, conditions, WHERE condition , KBA , BC-SRV-APS-GKE , Generic CDS Key User Editor , Problem