Yes? Wtf do you mean? Does UN secretary general asserting his own opinion through a deputy spokesman does not equate to the UN rejecting shit.
Antonio Guterres is the Secretary General of the Secretariat. He does not speak for the UN on policy. Which, is exactly why your quote from Forbes says “Guterres was against the use of cluster munitions” not “UN Rejects”. The UN hasn’t done shit. They’ve not made a rejection statement or vote. They’ve not “condemned” anything.
One dude, through a deputy spokesman, at a morning briefing, said he didn’t like it.