“LGBT-ness” is not one thing. It is a political/cultural category that lumps together several demographic categories. I continue to think gay men, at least, are probably (mostly?) born that way.
The Center for the Study of Partisanship and Ideology did a detailed report on the LGBT increase. Quote:
”When we look at homosexual behavior, we find that it has grown much less rapidly than LGBT identification. Men and women under 30 who reported a sexual partner in the last five years dropped from around 96% exclusively heterosexual in the 1990s to 92% exclusively heterosexual in 2021. Whereas in 2008 attitudes and behavior were similar, by 2021 LGBT identification was running at twice the rate of LGBT sexual behavior.
[...] high-point estimate of an 11-point increase in LGBT identity between 2008 and 2021 among Americans under 30. Of that, around 4 points can be explained by an increase in same-sex behavior. The majority of the increase in LGBT identity can be traced to how those who only engage in heterosexual behavior describe themselves”
There is discussion of some possibilities at https://www.reddit.com/r/SufferingRisk/wiki/intro/. I’d like to see more talk about these issues.