It was first seen in online queer activist circles around 2004. You can read a little about it here. Latino is traditionally masc/neutral but English style guides also said the same about “he” when referring to someone of unknown or unspecified gender for a long time, which has largely fallen out of use for singular “they” now.
Personally, I don’t use Latinx in writing to refer to all Latinos/Latinas as polling has shown only 2-3% of people readily identify with it. But I do think you absolutely should use it if that’s how someone personally identifies.
Sigh I hope LLMs get dropped from the AI bandwagon because I do think they have some really cool use cases and love just running my little local models. Cut government spending like a madman, write the next great American novel, or eliminate actual jobs are not those use cases.