i dont consider myself altersex/salmacian, seeking worldbuilding ideas from people who do

i'm returning to an old worldbuilding project i made in highschool. the people in it were constructed unnaturally and don't have the same biological limitations as regular humans, so they have 4 natal sex categories: the typical perisex female and male, in addition to an androgynous sex (i call them ambale in my notes) and a neutral sex (likewise dubbed neutrale)

i have a general idea for what a perised ambale person would look/be like (bigenital, capable of both becoming pregnant and impregnating others, capable of breastfeeding, both feminine and masculine secondary sex characteristics) but i'm stumped for ideas for neutrale individuals. nullo seems the most obvious to me, but that would only be what their genitals look like and not their other sex characteristics

if you were born as a neutral 4th sex, what would your ideal primary and secondary sex characteristics be?