Not at all! They/them/their is mostly used to talk about several people, it has also been used as a singular pronoun since the dawn of time! Shakespeare did it, for example! Most of the time, even if one is cisgender, you'll talk about them with they/them/their pronouns if you don't know their genders. Also transgender people generally use binary pronouns. Trans men use he/him/his pronouns and trans women use she/her/her pronouns. The people who would use they/them/their pronouns are non binary people, which includes agender or gender fluid people, for example. Also there are a lot of gay celebrities who invented yesterday to shape today's world. For example, Alan Turing, the man who invented computers, who was openly gay, in a period where same-sex inter****** was illegal and homosexuals were persecuted. He died by suicide, and it's commonly thought that this was due to homophobia. So yeah, someone you deem as "cringe" also contributed to a big aspect of today's technology by inventing the first ever computer.
And no, LGBTQIA+ isn't from left culture. Scientists recognized transidentity and non binary identities to be legit.
Here are some articles to understand this better: https://en.wikipedia.org/wiki/Gender
https://en.wikipedia.org/wiki/LGBTQ
https://en.wikipedia.org/wiki/LGBTQ_rights_by_country_or_territory