Polyamory and polygamy dates back long ago, all the way back to the B.C. era.
Ancient Romans had same-gender marriages.
Homosexuality was very common and acceptable in Ancient Greece.
Loki, an ancient Norse God, could change his sex, making him the oldest case of gender fluidity. He even gave birth to various creatures.
Singular they/them pronouns date back to the 1300's, making them one of the oldest English pronoun sets.
Many societies and cultures have a third gender they worship. As you can imagine, third gender is not new.
An ancient tomb in Prague was uncovered where a male corpse lay wearing clothes generally reserved for females.
There have been various paintings and figurines uncovered from the Neolithic and Bronze Ages of people with woman's breats and male genitals, or some without any visible genitals.
Michael Dillion was the first person to have sex reassignment surgery. He had it done in 1946.
Sweden became the first country to allow legal name change and hormone therapy to transgender indivuals in 1972.