I think his policy is sensible enough.
You can't have (often) left wing teachers deciding for themselves what to teach kids about sexual orientation or gender.
That's just going to result in indoctrination with the teachers forcing their politics on the children.
If you don't have rules in place, some teachers will take advantage thinking that they are being enlightened and progressive to tell kids that they may actually be a girl / boy regardless of their biology and maybe they need to go on puberty blockers.
Note that homosexuality can still apparently be mentioned in lessons.
It's not about "don't say gay", it's about don't force your left-wing politics on children. That's not the purpose of schools and it's unethical to do it.
https://flaglerlive.com/dont-say-gay-extended/
"But the rule requires that teachers shall not “intentionally provide” instruction on sexual orientation or gender identity in fourth through 12th grades, unless such instruction is required by state academic standards or “is part of a reproductive health course or health lesson for which a student’s parent has the option to have his or her student not attend.”
The rule also extends the outright prohibition on such instruction to pre-kindergarten classrooms."