Assume that a country removes the sex category from its legal system and thus also from its passports. Just like the hair color or foot size are no legal category. Would this cause problems for its citizens to travel internationally?
I found that the 'International Civil Aviation Organization' standardising machine-readable passports includes the category sex in its formats (see https://www.icao.int/publications/Documents/9303_p3_cons_en.pdf). But would it cause problems if this category is not present on the passports of this country? Or could this circumvented by assigning the sex 'X' to all citizens?