As i understand for when some data is collected (I think for the census in Scotland?) and maybe in medical situations, there is sometimes a check box for "Sex" which is sometimes labelled as "Gender" and sometimes there are both.
So for Sex a trans person should pick their biological sex, but for gender they can self ID (so they may check female sex but male gender). But where it's only sex or gender they are likely to pick male for both.
so if everyone just checks their Gender ID instead of their biological sex, it immediately erases all trans people, and therefore they can't be identified as such. Which in many many respects is total bullshit.
But. Since there are no trans people - they don't need any special funding or treatment. It seems a bit of an own-goal to me.