What exactly s the religion? Like, if there's god's, there's a religion. What's the Greek one called? Greek?

The Greek myth religion is specificity called Hellenc, Hellenism, ect. (Yes, it is named after the greek women
Hellen of Troy).

I don't think there was a name back then, since it's one of the first religions. It's simply called Greek mythology now...
However, worshipping gods (Greek, Roman, Egyptian, etc) back then was generally called idolatry. You can look it up to find the exact meaning.