This gets it 100% backwards.
At current tech levels, gender reassignment surgery is just glorified mutilation. Transhumanism is about human augmentation, not incapacitation.
You don’t augment yourself in any way whatsoever by transitioning towards an ersatz version of the other sex. You become infertile and develop many hormonal and psychological problems. Actively pushing people into it, especially children, as seems to be increasingly happening in many Western countries, is evil.
Most techs that might be considered to be transhumanist are currently prospective, if not speculative. That said, things such as pacemakers and contact lenses should quality. Maybe even spectacles – the Renaissance Italian invention that allowed many scholars to effectively double their working lives. After all, affixing a thin screen of chemically and thermally processed sand in front of your eyes isn’t entirely natural.