Does anybody actually know someone who says they won’t vote for Biden but would vote for his replacement, or vice versa?

I don’t. Every Democrat I know personally is voting for the Democratic nominee regardless of who it is. And how can we compare Biden to this hypothetical replacement when there is no consensus at all about who this would be?? The press will immediately tear apart the replacement no matter who it is.

I can't vote for Biden on account of the genocide, but I would really like to vote against Trump, so if they bring in someone who isn't actively paying for genocide I'd be thrilled and world definitely vote for them.