So Eternals are advanced androids but we know Thanos isn’t. I mean hit arm and head got chopped off. They would have noticed if there was mechanical parts inside. So maybe arishem lied and made biological Eternals first(The Etenrals of Titan or maybe even more who knows). Just like the Deviants he lost control of those Eternals and decided to only make the android ones from there on out. Also maybe other deviants have evolved even beyond that of the earth ones. Leading to interbreeding on some cases and that’s how you get Thanos. Or They follow the comics and the Deviant gene is just in those first Eternals and sometimes activated. TBH I didn’t feel like Arishem was lying to them though when Sersi was finally given the truth. So yea I interested in seeing how they explain how Thanos could be a Eternal as presented in this film. I guess him just being an Eternal is possible and he altered himself and that not his natural look. Maybe get a human Josh Brolin in a flashback with eros. Though I don’t like the idea at all.