At most Kamala only "lost" 2.1 million voters to other candidates this election (realistically it's probably around a million). If that's the case then 5.9 million voters voted for Biden in 2020 and nobody in 2024 but still casted a ballot. Now maybe that's because of Gaza but from my experiences with the American electorate I highly doubt that the majority of those people are refusing to vote for Harris because of Gaza, refusing to vote third party, and yet still voting. I think if Americans had coherent anti-genocide politics then the anti-genocide candidates would have seen more growth than 5% of Harris' losses. I don't believe Americans have coherent politics though so I doubt most of those voters were taking a principled anti-genocide stance when they didn't vote for anybody.

This isn't to say that abstentions or votes for other candidates because of the genocide could not have played a significant role in the fucked up math of the American electoral system, merely that it didn't drive her huge loss in the popular vote from Biden's victory in 2020.