I think a more charitable read would be they are claiming that Israel's geopolitical rivals have undue influence in certain UN organs and are using that influence to unfairly single out Israel.
Its not exactly a crazy claim. The UN is a political entity, its not above the influence of geopolitics. The former secretary general of the UN, Ban ki moon at one point (quite a while ago now) said that "Decades of political maneuvering have created a disproportionate number of resolutions, reports and committees against Israel".
The thing is that if not one single country agrees with you it kind of goes beyond just "undue influence".
It's a bad faith way to approach this argument, so asking logical questions won't make a difference and will tire you out. That's the core strategy behind that behaviour.