Yes for the purposes of understanding protections under the EA - “sex” as used in the statute , means “birth sex”, this means that people female at birth have separate protections from trans people who are protected by gender reassignment. That does not mean that trans women are not legally women- cannot change their legal sex. They can and they are legally women* if they possess a GRC.
The Supreme Court was very clear on that, they were also very clear that they were not making any judgements about what “sex” actually is/ means, they were just interpreting the use of words in the EA 2010,
Really important people understand this,