[rcxdude]

There is some evidence that hormone balance in the womb (including from the mother) can affect gender and sexuality. It's not impossible that it would also have an effect a little later as well, while the brain is still very plastic. I think the strongest version of the immutable gender/sexuality idea (that it is entirely genetic) is almost certainly false. My hottest take (mainly from my own experiences) is that it can perhaps in some cases be mutable a lot later than people think (which, to be clear, is a very different thing from it being a choice or controllable, and even if that were true, it would still be a valid choice).