If it were me, I'd do something like not really focus on what their actual "real" sexuality is unless it is somehow relevant to the plot. Then if it is so something like make them a 1 or a 5 on the Kinsey scale instead of a 0 or a 6.

I don't think games should be required to do, I'm not trying to force some sort of universal bi/pan agenda. I'm just saying it personally annoys me when I am locked out of pursuing a character just because of the gender I happen to be playing as because I typically don't play games multiple times. It also annoys me when games don't allow you to pursue all characters. Like in BG3, as far as I know, all characters are bi/pan but not all are poly. The game forced me to pick between Astarion and Karlach, for example. I put 100 hours or so into the game before I quit. I'm not willing to put over 100 more hours into it just to see what would've been different. It's just a waste of my time.

An alternative approach is only having "sex scene" type content gated behind gender, but everything else can still be seen by friends. E.g., anything a character would eventually tell a lover they still tell close friends. Which is still sort of annoying but not really as bad because you can easily just look up a sex scene, but experiencing things like dialogue and special quests in game isn't comparable to looking it up on YouTube.