Unknown gender or gender unknownness/unknowledge: having an unknown gender identity or expression; being unknowingly gender identified; when one’s gender/s is/are not known; different from being uingender in the sense that you don’t define yourself under one gender term.

The flag is based on “none”, “neither”, “neuter” and “both” flags, while genderunknown is based on genderneutral. I saw this symbol in PGo Pokédex, as for pokémons that are unknown-gender (sometimes considered genderless).

I guess we can call this mysterious gender or gender mystery too. – Ap