I agree it doesn’t mean the whole of the UN & its work can be discredited, I’m sure they do lots of good work.
What it does mean though is that they aren’t necessarily as neutral in their reporting as many people assume they are. They have longstanding links to Hamas, they have local workers that are sympathetic to Hamas goals.
They aren’t some completely impartial organisation and that is important to be aware of. People don’t expect the IDF or Hamas to be impartial but some assume the UN are completely neutral.