Or what biological sex is or anything else.
It's really really important that people understand that the court was 100% clear on what biological sex is.
The way to determine someone's sex has been defined in law since Corbett vs. Corbett in 1970.
The SC was entirely clear in it's judgment - section 1, entitled "terminology", paragraph (7):
We also use the expression “biological sex” which is used widely, including in the judgments of the Court of Session, to describe the sex of a person at birth, and we use the expression “certificated sex” to describe the sex attained by the acquisition of a GRC.
It's intentionally misleading people if not actually outright lying, to say the court was ambiguous about what "biological sex" means.