Sexless Flag
Sexlessness: absent/null sex identity; an umbrella term for lacking sexed characteristics or qualities (planned/desired or not), such as in nullosex (nullogenital, nullogonadal), asexed/assex (agonadal (gonadal agenesis), agenital (genital aplasia), ansex (angenital, angonadal, sterile)), nonsexed/unsex(ed) and desex/ed (i.e. eunuchs).
I mentioned it gonads and genitalia (also known as “primary/secondary” sexes), but this could also apply to hormonal, phenotypic, genic/genetic &/or genotypic/chromosomal/chromosomic sexes in some levels (karyotype, sex genes, chromosomes, genotype, phenotype and body/corporeality), e.g. you could identify as sexless because you are X0 intersex, have hormonal depletion (hypohormonal or hypogonadism) or sex paraphoria (i.e. indifferent what sex you have).
Reminder biosex (biological sex) can be also mental / psychic. Note this term isn’t the same as genderless or asexual.