Please note that I'm using "queer" as a generic term for all of those people who don't fit into the neat little box of heteronormality. And I just wanted to say that I've encountered a number of you guys (and gals and otherwise) as I've made my way through the Oz fandom and you've all been awesome.
Some people wonder if any queer characters made it into the Oz stories. There are those who point to the Scarecrow and the Tin Woodman as a gay male duet. Though I wonder how that would work because even though they have gender (they both identify as male and use the male pronouns) they do not have sex (biological or anatomical sexual characteristics). Unless there's something that Baum didn't tell us...
Though Baum did avoid even heterosexual romance for much of the series. He was writing mainly for children and you know how kids can be about "mushy stuff." Scarecrow of Oz is the first Oz story to feature romance as a plot point. A few books later, Baum gleefully skewered romantic tropes of his day in The Tin Woodman of Oz.
I've pointed to Tip/Ozma as a transgendered Oz character a few times. Although we meet him as a boy, the course of the story includes a sex change into his true form, that of Princess Ozma.