This is not a hill I’m willing to die on, I’ll hear other takes, but imo the term ‘straight-passing relationship’ is not intended to refer to a relationship with a cis man and a cis woman who are both queer. Straight-passing relationship to me refers to couples like, one or both is nonbinary, gender-fluid, closeted trans and only out to their partner etc. Or a sapphic couple with a butch that often passes as a man or a gnc couple that looks like they might be a cis man and woman but actually aren’t.
Seeing a bisexual man and a bisexual woman call their relationship straight-passing feels wrong to me. They themselves might straight-passing, but there’s a difference between an individual person being straight passing and a relationship being straight passing. Their relationship is actually, by social standards, straight, even though the people in it are not. I’m not invalidating queer people in opposite gender relationships, they are still always queer no matter who they date, but calling a relationship between a cis man and woman queer feels wrong to me.