Melissa Scott has done some lovely sci-fi with bi characters. I really enjoyed Night Sky Mine although I can't remember if the main character identifies as bi; she's some flavor of queer and is a teenager, as I recall. Dreamships and its sequel is also excellent and the main character is a woman involved with a woman; the sequel, Dreaming Metal is also great and has great queer characters.

I also recommend the Murderbot series to everyone right now. The new one is coming out in August! Murderbot identifies as ace, but there are bi and polyromantic and nonbinary and otherwise queer characters all around and it's a really great and fun series.

A Long Way to a Small Angry Planet is quite good and there is a happy queer romance in it.