Trump is a clear supporter of the genocide. He wants Israel to destroy Palestine and he wants the US to do more to help them accomplish this. Harris is nowhere near as bad as this. She's not going to withdraw support for Israel, but she's at least going to try to rein them in and return to the pre-war status. Not great, but realistically the best that we can hope for with how supportive our politicians are of Israel in general.
These are the only two people that have a chance at the White House. If you don't want to support the genocide, don't waste your vote on somebody that is absolutely, without a doubt, going to lose. Instead, use it to vote for the one candidate that is possibly able to win over the person that is explicitly, unequivocally supportive of the genocide.
In my eyes, not voting for Harris is supporting the genocide. Anything that allows Trump into office is supporting the genocide.
The UN is not meant to be a world government. It's meant to be a forum that allows all countries to maintain a bare minimum of diplomatic relations. The overarching goal is to prevent nuclear war and prevent WWIII.
It's predecessor, the League of Nations, was meant to prevent WWII and had some teeth to help enforce their decisions. The result was that it collapsed quickly and did very little to prevent another global conflict.