This is a very confusing stance, you’re advocating for not voting while not being a US citizen so you can’t vote??
And you completely misunderstand first past the post voting. You have it in the UK too. It’s how labor got elected, your far right party split the conservative vote. The risk here is that due to the US’ electoral college system a select few states (incl. TX, NC, GA, FL, VA, NV, ME not just the rust belt strip) will decide the election. Thus for those states, someone who could vote must vote for the Dems.
Any possible vote not for the Dems will help the Repubs get closer to clinching those close states, whether it’s no-vote or one of the virtue-signaling 3rd party candidates. (Yes, they only split the vote and are worthless for reducing harm, build 3rd party from local up)
Only one of two candidates will win thanks to FPTP. Both candidates will continue to enable genocide. But one candidate - Trump - will target trans people and will target women and will target minorities at home. So if you are a US citizen who can vote, you do the proper ethical thing: you vote for harm reduction via voting for the Democrats.
A vote is not an endorsement, you don’t have to feel tied to it; it’s an infinitesimal push to a better atmosphere to advocate for the end of the genocide. If Trump is in power left-leaning people will be split putting out fires: trying to keep trans people alive, trying to get women proper healthcare, trying to keep minorities from being rounded up. There will be less bandwidth for stopping the genocide, much less pushing for more progressive change.
In short, the only ethical move is to vote if you’re a US citizen to mitigate harm and improve the progressive landscape to be able to maximalize effort towards ending the genocide. The only ethical move if you’re not a US citizen is to not advocate for not voting for the democrats; might as well be a Russian bot at that point.