This is from the Consolidated guidelines on HIV, viral hepatitis and STI prevention, diagnosis, treatment and care for key populations
https://iris.who.int/bitstream/handle/10665/360601/9789240052390-eng.pdf?sequence=1
Key populations: defined groups who, due to specific higher-risk behaviours, are at increased risk of HIV, viral hepatitis or STIs irrespective of the epidemic type or local context. Also, they often have legal and social issues related to their behaviours that increase their vulnerability to HIV. These guidelines focus on five key populations: 1) men who have sex with men; 2) people who inject drugs; 3) people in prisons and other closed settings; 4) sex workers; and 5) trans and gender diverse people. People in prisons and other closed settings are also included in these guidelines because of the often high levels of incarceration of the other groups, and the increased risk behaviours and lack of HIV, viral hepatitis and STI services in these settings.
And this is what they say about including 'trans and gender diverse people' in the key populations.
Transgender people are around 13 times more likely to be HIV-positive than other adults of reproductive age. In some regions, transgender women account for disproportionally large shares of new infections, including Asia and the Pacific (7%), Latin America (6%) and the Caribbean (5%). HIV prevalence among transgender women is estimated to be 28.4% in Eastern and Southern Africa; 13.5% in Western and Central Africa; 22.2% in Latin America; and 23.7% in the Caribbean (UNAIDS, 2020). Little data is available for transgender men and other transgender populations regarding HIV epidemiology.
Note the switch from 'transgender people' in the first sentence, to 'transgender women' in the second, then at the end the acknowledgement that they have no data for 'transgender men'. Also the geographical area that these high infection rates relate to is limited and doesn't include Europe, North America or Australasia where a very different demographic are identifying as transgender.
If the WHO's concern is about HIV in male transsexual sex workers in Latin America, the Caribbean and parts of Asia, then they shouldn't be making guidelines which will be used totally inappropriately for teenage girls in countries like the UK.