I think this decision was taken some time ago. There's an articel about it from July 2019. c-fam.org/friday_fax/un-women-to-replace-women-with-gender/?fbclid=IwAR0DGifOQX8bjauQns5gXG_b7V_RtI_WuzOz5auzax-kvXLy3niOcxXvwm4
It seems to be the mechanism to include trans women as part of their focus.
Quote:
Mlambo-Ngcuka claimed “sexual orientation and gender identity” are core values of the Sustainable Development Goals, signaling that billions in aid meant for women may be redirected if UN agencies take it upon themselves to redefine the internationally-agreed goal of “gender equality” away from women’s rights.
Mlambo-Ngcuka said, “we push the envelope every day” on what constitutes “human rights and fundamental freedoms.” UN member States have rejected the claim that “sexual orientation and gender identity” are a part of any treaty obligation under international law.
Mlambo-Ngcuka admitted a lack of support from the General Assembly but said her agency would push until “equality of all genders becomes the norm.” She said the UN must work to overturn laws in the seventy nations that still do not sanction homosexual sex.
The event was organized by Outright, a homosexual-transgender advocacy organization.
End quote
If you look at their home page the message on there doesn't seem to be quite so obvious. (Which doesn't mean lobbying isnt going on in the background.) www.unwomen.org/en/about-us/about-un-women
I am sure there was a thread about this at the time.