Ok, I have a suggestion, given that this is a very clear change of tactic and yet again, it's a linguistic trick.
We do not need to press 'you can't change sex'. The immutability of sex is pretty self evident at this stage. Besides which, the cult language has done what we predicted about a year and a half ago, and shifted away from changing to confirming, so the person has always been 'female', etc.
The TRAs are doing this - 'Of course you can't change sex, but actually sex is a wide variety of possibilities that are almost too complicated to clearly define, and essentially pointless for all practical purposes'.
The best counter to this is - There are two sexes, and for some very significant things, SEX MATTERS.
Because this is, and always has been, the crux of our argument. Keep saying it. Don't let them own the narrative.
Sex is real, and sex matters.