From their guidance notes:
Measuring gender identity is an evolving topic. On 5 September 2024, Emma Rourke, Deputy National Statistician, wrote to Ed Humpherson, Head of the Office for Statistics Regulation (OSR), to request that the gender identity estimates from Census 2021 are no longer accredited official statistics and are classified as official statistics in development. The change in designation was confirmed by OSR on 12 September 2024. The ONS requested this change in designation after patterns were identified in the Census data that suggested that some respondents may not have interpreted the Census 2021 gender identity question as intended, notably those with lower levels of English language proficiency.
Well, yes nonsense in = nonsense out.
What a total and utter waste of time and resources.