My neighbours don't have a catflap and their cat is out overnight. We got a door camera a few months ago and it always picks him up at about 11pm coming into our slightly covered porch area and sleeping on our doormat until about 5am, when he wanders off. He's not a young cat, they've had him since we moved here so he's at least 10.
It's starting to get pretty cold at night. I wondered about putting a folded blanket down for him or something so he's more off the cold floor. But I guess he's been OK up to now, before I knew about him visiting.