I'm old enough to have been the guinea-pig class when it came to the national curriculum.
I may not remember my school days with perfect clarity, but I didn't learn about 'trans' at school. Section 28 must have been at play when I was at school and yet my best friend, who was gay, was mostly supported by the school. So things have obviously improved since then.
We learned about sex, but it wasn't 'oh it's fun' as some posters who shudder teach sre/give advice to young people on sexual health seem to push. It was STDs are a consequence of sex- here's how to protect yourself. Pregnancy is a consequence- here's how to stop unwanted pregnancy.
I would have hoped as it's broadened to be more inclusive (without section 28 for example) it would still keep that safeguarding message. Here's how to protect yourself if you take part in XYZ sex act. Here's how to protect yourself from revenge porn.
It's not a general theme in primary but it seems to me that some people think sre is there to have a nice little cosy Anne Summers like chat about kinks etc. It shouldn't be like that. I didn't find out about fetishes or anything like that in sex education and I don't think that's what it is there for.
I think actually, where trans is relevant is not in the SRE part, but in the PSHE part of the curriculm. Along with tolerance for other religions, races and sexual orientations. You don't need to follow Islamic orthodoxy to show tolerance and respect to Islamic people and you don't need to know the ins and out of gender ideology to do likewise to people who believe in gender.
As trans people are fond of saying, it should be acknowledging that they exist and deserve the same respect and consideration everyone else gets. No more, no less.
And it doesn't need to be covered in great detail, in either SRE or any other area of the curriculum to do that. We don't teach all the world religions, but we still manage to get across the tolerance message for them, why is gender ideology this special case where everyone must know the ins and outs of a very specific, spiritual belief system?