We think that the focus on 'afab' is very confusing and likely disrespectful to other people's gender.
We'd say it's not really possible to be attracted to a gender assignment and probably what you mean is genitals or some other physical features.
Most nonbinary people who have worked hard to get rid of or distance themselves from their gender assignment are probably not going to appreciate you finding them attractive based on a gender assignment.
Genital or other physical features attraction is probably okay and much better than saying you are attracted to a gender assignment. If you are going to call yourself 'sapphic' then unless you are legitimately only attracted to women and lesbians, regardless of genitals or other physical features, then we suggest just explaining your attraction rather than using 'sapphic' by defining it as being attracted to people who aren't women/lesbians but who have vaginas and not being attracted to women/lebians who have penises as that's just invalidating and transphobic, nonbinary erasure etc.
Hello Kitty, now with mallet.