gender-archival:

Non-x, also known as Binary X, was coined by Wiki user Dreaming-apples on March 5, 2021.

Non-x is described as “You are in the between agender and non-binary”

There wasn’t a flag in the original coining post.

Links:
Wiki: https://lgbta.wikia.org/f/p/4400000000000104020 + https://archive.vn/NuSCA