A long time ago, one of my friends suggested to me that the world would be better off if there were only one human gender: if everyone was hermaphroditic, say. "It'd eliminate gender discrimination. What good do gender differences do us?"
After writing A Rational Arrangement, where societal and legal pressure to conform to a heterosexual, monogamous ideal was overwhelming and a major source of conflict for the characters, I wanted to write about a much more open society in The Moon Etherium. I made a magic-rich setting where all the characters had easy access to a variety of powers, including shape-shifting. In their society, gender is a choice: a choice one can change on a whim, and doing so is unremarkable. Many characters in The Moon Etherium strongly identify with a particular gender and do not change it. Most identify as male or female. But some identify as neuter, and some identify as a mixture, and some change randomly, and all of this just happens and no one much worries about it. One of the challenges of writing the story was presenting this without giving it undue emphasis, because to the characters it's trivial.
In a similar vein, there's no societal stance on "this is the right kind of sexuality" or "the right kind of relationship". The female protagonist, Ardent, had a wife for many years, and is now attracted to the male protagonist, Miro. She never reflects on her sexual orientation because of this, because her society doesn't care. Straight/gay/pan/etc are all ordinary and acceptable and the society doesn't feel a need to categorize them. The protagonists do have an explicit conversation about relationship types (monogamy, polyamory, etc.), because 'we should agree on what our relationship is, since there is no default.'
The Moon Etherium's romantic subplot is M/F and between two people, so in a sense the LGBTQIA+ and poly-postive aspects of the setting are not integral to the story. The main protagonists strongly identify as male and female, respectively. There were various reasons why I wanted to write their story this way. Part of that was that my protagonists live in a society without gender roles, and I wanted to distinguish between "gender roles" (which is a meaningless concept to them) and "gender identity" (which they do have, although it's more fluid for some than others). I didn't want to write about a society where characters took on male forms to do masculine activities and female ones to do feminine activities (though that could be interesting!) But I did want one where the people still felt that male/female/etc. had some meaning. Because gender is fun.