Until now, if you built a Custom Property Editor and wanted to enable users to map upstream mergefields to various inputs of your CPE’s underlying action or screen component, you could only get access to manual variables. Salesforce in general is encouraging flow builders to move away from manual variables and let Flow handle things automatically. So it has been important to enable CPE developers to have access to automatic references.
That’s possible starting in Spring ’21. Here’s the release note with the syntax:
We intend to upgrade the Flow Combo Box that can be found in Flow Screen Components Base Pack to incorporate this new data access so that all upstream values will be visible and we can always use help from the community. If you’re an LWC developer and interested in helping out, please post a comment.