Hi Olivier,
In a custom entity, I created a Text field for FullName, and a Person field for PersonName.
Then I opened the entity in Excel, I found that the PersonName includes Given name, Middle name, Surname. While FullName is just a text field.

When I created an app based on this entity, I was asked to enter Given name, Middle name, Surname for each field. While Fullname is only one field.

So my understanding is that if you want your user to enter the exact name with Given name, Middle name, Surname, a Person field type might be your choice.
Please try this on your side, hope it can be a reference for you.
Best regards,
Mabel Mao