Fiori on S/4 HANA - interpretting the Fiori Apps Library

Hi Fiori friends, and Fiori people at SAP,

Please could you help me to answer this question around Fiori apps on S/4 HANA:

I am looking specifically at the "Approve Purchase Orders" app in the Fiori Apps Library

Having selected the S/4 HANA option on a previous app (My Leave Requests v2), I now get a pop-up on PO Approvals saying "This app does not exist in SAP S/4HANA, on-premise edition":

I can see the backend component is stated as "Fiori for SAP Business Suite - Latest back-end version", and there is no drop-down here for S/4 HANA, as there is for, say, Track Supplier Invoices:

Does this mean that Approve Purchase Orders is NOT available at all on S/4 HANA? What is the reason for this please?

Thank you,

Lindsay