Get rid of the GRA/GRC altogether. You can't change your sex.
Recognise people might also have a social sex, which could be called gender if it seemed everyone would understand that.
If a form asks for your sex, it means your legal, natal, XX/XY sex, because that is what it needs to know . When it doesn't matter, use whatever gender you want.
Passport and driving license can use your gender because that's about identifying you.
Sometimes they can ask for both so that your doctor's computer can send out letters saying 'Dear Ms Jones, don't forget your prostate check' when necessary.
Spaces might be segregated by sex or gender, but it has to be completely clear which is being used. If sex is being used, there has to be a third space. Certain institutions have to use sex. (Schools for instance. Public toilets.) So a nightclub could use gender if its clientele would prefer that. Or I was thinking of the poster who said that, at their uni, the sociology building loos were by gender and the physics ones by sex.
This means we get rid of a legal fiction which is becoming dangerous and people who want to be recognised in a particular social role can do so. Everyone happy.