3360956 - Extended Custom Field is missing in data source extension function after adding Custom Field to application

Customer has created a Finance (FI) custom field, and want to add this field for Customer line item management.  This works, but the custom field is missing in "Data source Extensions function" in "Custom Fields and Logic" App.

• S/4Hana Cloud
• Custom Field
• Custom Data Source Extension

1. Create Custom Field YY1_XXXField
2. Enable oData for Post Journal Entries
3. Add Custom Field to Post Journal Entries app
4. Create New Data Source Extension YY1_XXXExt for FAR_CUSTOMER_LINE_ITEMS (CDS View I_JOURNALENTRY).
5. Open data source extension and Custom Field YY1_XXXField is not in it

The “Journal Entry” node in the data source extension “YY1_XXXExt” is bound to the CDS view I_JOURNALENTRY, however, the custom field "YY1_XXXField" is not available in the CDS view I_JOURNALENTRY because this view is not registered for extensibility (TX: scfd_registry). 

The business context FINS_CODING_BLOCK allows to extend the CDS view I_JOURNALENTRYITEM, but this CDS views is not available in the data source extension tool, because I_JOURNALENTRYITEM is connected via a 1-to-many association (_JournalEntryItem in I_JournalEntry). The Data source extension tool supports only 1:1 associations.  

There is no way to make the extension field visible in the Data Source Extension.

https://help.sap.com/docs/SAP_S4HANA_CLOUD/0f69f8fb28ac4bf48d2b57b9637e81fa/04cc9e89e0214fb3b9ae29e3b5854f4e.html?version=2308.500

Custom Field Data source extension , KBA , BC-SRV-APS-EXT-FLD , Custom Fields , Problem