Ok, Alex, so I understood, but at the same time, above, you explain to me that it's normal for me to encounter an error because I added mandatory fields to the second form.
Which forces me to disable this interesting feature.
I think you do not realize the problem because here on UNA the profiles are very minimalist.
But nobody will be in this case on a site he built, and I think this error will raise the same question all the time, you already have an example here https://una.io/page/view-discussion?id=705

What I would like is an option that allows me to complete "AccountName" in the first form, then be redirected to the second form containing "FullName" == "AccountName" already completed, see grayed out, so that I can continue to fill the other fields of the profile.
You understand ? So, that would be perfect.