On the first step of a data transformation feed, there should be a separate 'Source' option. Right now the option is called 'Transformation'. This isn't consistent with other feed types and it should be. Select a source, hit next, do some transformation is the right flow.
Data transformation doesnt have a “source” option because you choose your “sources” when you transform.
XML Ingest has a source option which you can then transform and create your script. We are looking at updating the “XML Ingest” transformation flow to be the common usecase model for our feed creation in the future with the A2A work. Its probably worth noting that this should be renamed to “Advanced Transformation” rather than “XML Ingest” as its not specific to just XML files.