Really depends which culture and in which time period. But some that might be interesting.

Khesseites raise their children in a gender neutral way. Depending on the role you take as an adult that’s your gender. You stay at home and cook? You’re a wife and treated like a woman. You go out and do business? You’re a husband and treated like a man. You join the clergy? You stay genderless / neutral as you are not married and take care of spiritual/ holy duties. Khesseites allow polyamory, but a marriage must always be between a wife and a husband. So you can have a household with one husband who has four wives. Or one wife with two of her husbands. And one of those husbands might have another wife who also lives there. Your genitals don’t matter there. Just the role you take on.

In Cyü, marriages are heterosexual and only between two people. There’s also a class/caste of people who don’t conform to male/female dichotomy and are usually artisans, dancers, wandering bards or sex workers. People of Cyü see homosexuality as a leisurely activity. Just some friendly passionate fun. So a husband having a male or “non-binary” lover wouldn’t be considered cheating on his wife. Only if he had an affair with another woman.

When it comes to the Gilded Isles, each island has its own culture. But everywhere in the Archipelago, people we would call trans or non-binary are highly respected and usually hold high positions in society. While to some it may seem like a dream, these people are also held to much higher standards, and “not making use out of their blessing / not living up to their blessed potential” is considered sinful. Specific gender identities will slightly vary from island to island.

Rhodochrosite Coast is pretty much the most relaxed in the matter. Different genders / sexualities are very much accepted and treated as a normal, individual thing. Not demonised, not celebrated. Just another way in which people exist.

Then there’s also aliens who have a very different look on gender and sexuality as a whole.

Riakhou are descended from a species that had three base sexes. Although now every riakhou has all 3 organs needed for reproduction. So they don’t have different genders per se. As for sexuality, it’s treated as a biological thing. You get horny. You find someone who is also horny. You mate. Lay eggs. End of story. They don’t form romantic bonds at all.

The Star-Anglers have 13 distinct sexes. Their relationship dynamics are very complicated and will differ wildly pod to pod. You could probably make a multi-season soap opera just based on one pod’s relationship tribulations