Re the title: According to the OP, Stonewall did a survey. The first few posts questioned the validity of the survey, alongside questioning anything that Stonewall does really.
The question of whether more young people today feel relaxed enough to say they are gay-as in only want intimate relationships with others of the same sex is a good one. Certainly compared with earlier years, it’s much, though not entirely, safer to do so.
People, young or old who are gay have not and do not claim to have changed sex.
Discussion often moves into trans, usually TIM, who having declared themselves women, claim lesbians (or any women), are homophobic if they turn down intimate relations with them. They never seem to grasp that a TIM having sex with a female is a heterosexual act and if she is unwilling, it’s rape, not homophobia.
Similarly if a TIM wants intimate relations with another TIM, that’s a homosexual act, and if one TIM is unwilling, it’s rape not homophobia.
Nothing to do with more young people feeling safe enough to admit they’re gay. (You don’t turn gay, it’s not a metamorphosis.)