Atheists commonly use an argument like "well I don't believe in Zeus or Thor or the Flying Spaghetti Monster so God must not exist either"
It's not an argument per se. It's more of a way to point out the vacuousness of theism. There are a literally infinite number of things that might exist that we can't see or detect in any way and have zero evidence for. The point is to ask, why do you pick out just one of those things to believe in? The evidence for all of them is precisely the same: zero. So how do you choose among them?
It would be like someone saying "well I don't believe in the ether, so gravity, electromagnetism, quarks, blackholes, etc...must not exist either".
No, it would be nothing like that. There is zero evidence for ether, while there are varying levels of evidence for those other areas. You might want to get a better grasp on how analogy works; just a friendly piece of advice.