like 6% have ever actually had sexual contact with someone from the same sex, which closely tracks the historical rate of the gay population from a lot of long term surveys (it's about 5%).
i think there's a social contagion/social signaling effect here with Gen Z where people are saying they are bi, but they have no intention of ever following through with a same sex sexual encounter. if they break this down by demographic you will see that it skews heavily towards college student women stating they are bi. you see this in survey after survey (one article included below.) that's a social contagion/social signaling effect IMO.