I don't doubt many were motivated due to Gaza. But it's not clear that those numbers are significant enough to affect the outcome. If all of them had voted Harris, would she have won? We'd need a better study to know that.
Yeah I don't have numbers, but anecdotally a decent chunk of Gen Z in my liberal leaning circles sat about because of Gaza. Like, the Muslims I expected, but the number of non-Muslim "allies" who sat out surprised me.