Need a fundamental understanding on list editing 🧐

Hi there,
My form has input fields whose values are saved as object in a list. Users can save a few such forms (add more objects with same schema) in the list as they hit ‘add more’ with a WITH_ITEM() in the update records flow.
But the below is not right:
On the second ‘add more’ button hit, fields values are inexistant.
Please can you explain what the right expression inside each field should be?