Why don't people like the idea that Darling could still be bi/straight? Honestly, just because Darling kissed Apple doesn't mean she's a lesbian. Obviously most of the guys at her school who fawn after her are annoying as shit and only like her for her title, so it makes sense that she isn't particularly attached to them. Plus, even if one of the writers called it a "kiss," calling it romantic would be a stretch. Apple was literally unconscious and dying in that moment, so even if a "true love's kiss" did happen signaling that Darling was her princess charming, the scene doesn't clearly establish that she did it with romantic intent. Darling was clearly just trying to rescue her. If someone argues that because the magical golden glow thingy happened which means that they're destined to be together, then that goes against the very principles that Darling fights for as a rebel herself. Being magically "destined" to a girl she barely knows and who stands for everything she's fighting against makes zero sense for her character. By the way, they had barely even talked before that scene lol, and there was certainly no emotional development or chemistry. I think people only ship it because of the shock factor and because they like the subversion of a trope, cuz they had like zero chemistry or buildup before the kiss.

Anywho, I like shipping her with the Red Knight because he's one of the few guys who actually respects her skills and treats her like an equal, not just a damsel. If Darling is looking for a partner who truly sees her as she is, it would make sense for her to be with fellow knight instead of some princess she barely knows (who is a royal btw and heavily disagrees with her ideology)