I literally did what you mentioned beginning at 0:26 seconds in the video I sent you
Anyway, the 2nd issue in my last post is actually this one, which was solved by enabling experimental options:
However, the bug report of this topic is still present. I'm sending you another video that hopefully shows you the issue more clearly. As a reminder, the Data Binding Picker of the API Workflow (or whatever it's called) doesn't show the subtable column. Not to be confused with the Data Binding Picker of Server Connect (front-end), which is the one shown in the documentation you linked