You're completely missing the point of the trolley problem:
Do you take an action that causes a direct harm, even if it's in service to reducing harm?
It's a valid moral stance to decide you will not personally perform a harmful action. That's not walking away from the trolley, that's refusing to throw the switch.
Your framing of the situation is false. Voting for Harris is throwing the switch and dooming Palestinians. Voting third party/not voting is not throwing the switch: you are not condoning the system that runs people over, you are not taking an action that directly harms people.
To be clear, throwong the switch is also a valid moral stance.
Personally, I believe voting for Harris prolongs our faulty political system. I voted for Kerry, then Obama (first willingly, then let myself be guilted into it). The Democrats have only gotten worse with time, and I won't vote for a party that represents me less with time instead of more.
"We didn't go far enough to the right" has been the excuse for decades and it continues to be bullshit. The people telling you the rules of the game are lying to you.
Leftist domestic policies don't win leftists, they win centrists, because those policies put money in the pockets of the working class. Improving Medicaid and food stamps, raising the minimum wage, UBI/federal job guarantees, building public housing, expanding unemployment, forgiving student loans, these all win lower and middle class votes.
Instead of any of this, Kamala and Biden said the economy is great.