Both UNESCO and the UN offer and sponsor good educational programs on the Holocaust, slavery, genocide, etc.
What pisses off the Zionists & Israel's lobby is when both organizations criticize Israel for it's genocide in Gaza.
In UNESCO's case, it's because they've blasted Israel for it's bombing & destruction of ancient structures & sites in places like Lebanon, Syria, Yemen, and even Iraq. In many cases those ancient historical sites carried artifacts and symbols denoting African presences etc. I posted about that earlier (even Bashar al-Assad of syria) kept those areas protected with funding from the UN & UNESCO.

In context: just imagine Chinese far-right nationalists bombing & destroying some MOGAO cave paintings just to erase those proving the African presence in the area during the 'Silk Road trade'. This is kinda what the Israeli military was being accused of doing etc etc.