This is awful. I hope this man takes legal action. We're going to get to a point where no teacher except one with a political agenda pushing an ideology will agree to give lessons on puberty.
What the school did in this circumstance is abuse the safeguarding system to make this man's life a misery and it worked because he's effectively given up teaching (except for supply).
Meantime, we have the 'school of sexuality education' (not sex, you note, sexuality) sending staff who have not gone through the same safeguarding checks as school staff into schools and this organisation has staff who have links to fetish websites. Which is apparently FINE. And parents being denied the right to scrutinise their resources.