S/4 HANA Cloud Public2402: How to enhance "Item data" within the "repair order" app in the launchpad

[sdig89]

Hello experts, 

We are working on the newest version of S/4 HANA Cloud: Public edition version 2402 and would like to enhance the "item section" in the "display repair order" application within the launchpad (Application ID: "TBT116RPO")

The requirement is to add new custom columns within the item section, which can be manually modifiable by users and whose content should be controlled later on during the SAVE operation (when creating or updating a repair order):

The controlling during SAVE operation can be done thanks to the Cloud BAdI "“Service document check before Save / crms4_serv_check_before_save", that's not my issue. 

My main issue right now is adding these new columns with the custom data.

First, when checking the application itself, looks like this is not a fiori application build in with the UI5 framework, but rather with the "WCF" framework:

Application details in the fiori launchpad

This is confirmed with the documentation found in the fiori reference library, where this app seems not to be a fully Fiori application, but rather a "Web Client UI application"

Application details within the fiori reference library

When trying the key user extensibility, in order to find the suitable "business context" to use to create new custom fields for the new columns to add at the "repair order item" level, somehow the key user extensibility tool does not provide a "plus +" icon (which normally opens directly the "custom fields and logic" fiori application with the suitable business context). The "Adapt UI" on the "repair order" application only seems to allow to move sections up and down: 

Key user extensibility not available at the repair order app?

Thus, I am wondering whether key user extensibility works on such Web UI applications, I guess not? am I wrong?

Since the key user extensibility "did not provide me" the direct access to the "custom fields and logic" app with the suitable business context, I started digging in SAP ADT and I felt like the I_ServiceDocumentItem data definition is the one "behind" the repair orders item list (service Object type = "BUS2000116") as shown in the example below: 

I_ServiceDocumentItem is the data definition behind the "Repair order" item screen

Based on this, I used the "custom fields and logic" app to create one new custom field "YY1_SrvItemDis" under the business context: "Service Item" which I have enabled on the "Service transaction item I_Service DocumentItem". This lead to extending the I_ServiceDocumentItem structure with a new custom field: 

Custom field added at the repair order item level

Then I used KeyUser Extensibility to add the new custom field in the "Item level" of a repair order/service order which worked well: 

Then when I tried to add the custom field to the "item list", with the "Adapt UI" feature, I can see the new custom field when clicking on "Add Column":  

The new custom fields can be seen: 

But then, after choosing one of these custom fields, they are not added to the "Item level" section table and no changes happen:  

Is this a bug in SAP Standard that I should it push it to SAP Cloud Public edition teams?

Or I am missing something to fuflill my requirement? Will I be able by following these steps to add the new custom field "YY1_SrvItemDis" as a new column in the item level at the "repair order" screen? Will this require from me to extend "R_ServiceDocumentItemTP" or maybe "C_InhRepairOpenRepairOrderItem" or maybe both? Or am I going into an incorrect direction?

Is my requirement "feasible" in a S/4 HANA Cloud public edition environment?

Thank you all in advance