it's cross sex hormones that can cause sterility, not puberty blockers.
Cross sex hormones on their own do not necessarily cause sterility.
Puberty blockers do not cause permanent sterility if they are stopped in time for the child/young adult to go through normal puberty.
But puberty blockers used before fertility, followed immediately by cross-sex hormones (which seems to be the normal progression once puberty blockers are given) are likely to create lifelong sterility. It’s not specifically either drug, but is the combination that causes the problem.
As for the case, interesting that those bringing it (and specifically JM) are claiming parental consent is now an acceptable alternative pathway, whereas this court case is about a circumscribed situation where the treatment is already under way and this is about continuation, not commencement of treatment.
I hope that GIDS do not jump to direct parental consent in the event they don’t win the appeal. If they were to do so, given the very specific statement before Keira’s case that they had never considered that a suitable model, it would be a deeply cynical move and would remove any doubt about the presence or absence of ethics.