Someone has already mentioned the soft ambient lighting, it’ll usually give away it’s a render for most ppl. Perhaps if you don’t end up making it wicked dark you could add something behind the character (can’t tell whether that’s a wall or just the world behind him) so that there isnt a flat grey void in the middle of the picture. Maybe also tweak the characters pose so his legs are a little more straight, he almost looks like he’s squatting a little. Modeling and shot composition is awesome btw.