The UN did not accuse China. Michelle Bachelet did. This is a common problem with these UN human rights abuse claims, where a single political appointee makes a claim, and the propagandists spread it as having full UN backing. They did the same thing to spread the sexual violence hoax for the Israeli Oct 7th propaganda. It’s not even the first time they’ve done this with the Uyghurs:
https://thegrayzone.com/2018/08/23/un-did-not-report-china-internment-camps-uighur-muslims/amp/