From Nature - affects fertility in both boys and girls treated in early adolescence: https://www.nature.com/articles/s41585-020-0372-2
From Lancet - importance of informed fertility counseling for trans young people: https://www.thelancet.com/journals/lanchi/article/PIIS2352-4...
While some may claim the resulting infertility condition that impacts young people given puberty blockers is the price worth being paid due to trans suicide rates, it is worth stating: it is not benign and it is not reversible.
The treatment side effects are permanent and are life altering for most people. Imagine a person finding out at 26 that they are infertile - it is a life impacting event that causes mental anguish, divorce in some cases, and even suicide.
Lets trust the science here.