I don't know if it's been directly confirmed, but Chloe Zhao essentially confirmed in an interview that they were not susceptible to the Snap due to their biology.

They cannot breed, so their unique physiology wouldn't count as life. So it does make sense that they wouldn't be counter as such.

They can't procreate? I know they're synthetic beings and all but we don't really know the details of their bodies enough to say they can't give birth

I know it's been confirmed in the comics that Eternals can't reproduce with each other, only other alien species