It is an old, old pair of synonyms.
No one is doing any subversion of language here.
NOW, "gender reaffirming care" is different. That is bastardizing language in an obscene way.
That is chopping off pediatric penises and creating false vaginas with plastic surgery. Etc. Then BSing everyone by calling your obscenity with a cool touchy-feely new name.
I absolutely disagree with that. They are absolutely subverting language, and the substitution of "gender" for "sex" is absolutely a novelty pushed by perverted leftists. Until fairly recently everybody knew that "male" and "female" were the two SEXES ... and that "gender" was something you dealt with learning foreign languages.
Remember "The Rocky Horror (Picture) Show"? Did they call the Tim Curry character "transgender" NO. They did not. The term was "transsexual".
"gender reaffirming care"
That term is indeed a bastardization of language, but it begins with the deliberate misuse of the word "gender".