Here’s a few threads about non-binary stuff in general. (@Laguz was our resident expert for awhile, so you might check out their posts first.)
How to write a social setting and characters that deal with non-binary identities respectfully can be difficult, but this post is going to focus on coding. I didn’t realize until I worked NB main characters into my WIP that there were some logistic differences to accommodate.
Terminology is different. Gender-based words for sexuality (e.g. heterosexual) don’t fit, so the terminology is androsexual/gynosexual (prefers males/prefers females). If a non-binary person prefers other people outside the gender binary, the word is skoliosexual, or there’s another one that I’ve forgotten.
In my coding I’ve actually got three different flags - the MC’s gender (which sets things like pronouns, affects which clothes are available to them, etc.); which gender(s) they prefer (which sets whether to show or hide flirtatious options with those characters); and an orientation flag (if the combination of 1 and 2 make them non-heterosexual, it affects the reactions of other characters.)
Attraction to others is a bit hard to code - given 3 genders (male, female, NB) there are 8 possible combinations. (All; none; 3 options of only one; 3 options of any 2.) I simplified it for myself down to male vs female (prefers male/female/both/none) and likes non-binary (true/false). Then I can check whichever one applies to whoever they’re around, or combine the two if I need to.
Identity coding is only difficult because it can overlap. If you separately code gender, orientation, and gender presentation (you only have to code whatever you’re using, but it’s nice to know which wardrobe your MC’s reaching for), you can make anything from a crossdressing gay man, to a hetero tomboy, to a pansexual non-binary femme.
The one thing I couldn’t sort easily was trans vs./and/or NB. If you try to fit trans into the gender slot, you end up with six options (similar to what happened with sexual preference.) So again, I made gender one of three options (male/female/NB) and split trans off into its own flag (true/false). Gender is what’s referred to the most, and I only check the trans flag if it’s relevant.