(I don’t remember if this was about anything beyond gender and orientation, if it is, I’ll add that later)
I kinda feel that because the Slayer mythos is so patriarchal that it’s somehow tied into cis womanhood to an extent (which is cissexist and intersexist and fucked humans are pretty binarist in the Buffyverse), so Buffy is probably a cis woman. (post Chosen might include Slayers that are not cis women because every potential was activated so trans boys/men or nonbinary people might have gotten their powers then).
As far as orientation, I think because of the Satsu thing in S8 comics, she might consider herself something like bi-curious, or heteroflexible or I think her canon attitude was experimenting/lonely straight person. I’m pretty sure those terms are various levels of iffy but she didn’t seem to embrace bisexuality because of Satsu, so... Maybe she will someday (once Buffyverse stops bi erasure in general).
(I do not think about Buffy much, so anyone is free to fight me on these.)
TL;DR Buffy is cis and not totally straight.