Apogender is subset of agender in which you feel not only genderless but entirely removed from the concept of gender.
Being “genderless” is still in relation to the concept of gender, being without gender or feeling void of a gender. Agender isn’t Apogender since it is still referring to the concept of gender. However, Apogender is a term used to describe someone who feels they are totally without the concept of gender.
The term can be considered a oxymoron, since it is given a label in the gender community, even given the term “gender” in its name, even though the person identifying as this feels as though they are entirely removed from the concept of gender. Because of this, many “Apogendered“ people don’t use this term or any terms at all, since what they feel is removed entirely of the concept of gender and does not have a place on the gender spectrum.