I'm not disputing whether or not a subform design such as what was posted will work, but I can say that it is possible to drill down that far. See image that results from
I don't recall that there was ever enough explicit info to help you with that but I'll look at your screen shots again. In my present view, I cannot see them.
EDIT - OK I remember now. None of that means anything if I can't see/associate the words with the object names. Far better to post text rather than some images. If I had the text, I would have Google translated it, but I'm too lazy to type out a language I don't understand.
I know about the nesting. My post was all about the syntax for getting there. Can't help with OP's specific situation if I can't associate the levels with the object names, let alone read Italian, so I made my own. However, I was able to put a subform on a datasheet even though you claimed (I think) that it cannot be done. Sorry if I'm confuzzed about your statement(s).