I got a 6 months male who has been used to freely wander outside.

I'm wondering about letting him go outside. I live at the second floor and share a balcony with my neighbor (a entrance balcony, which means that the cat could go out if someone opens the entry door). That seems dangerous for him.

I wanna point out that he's very happy cat, always playing, cuddling with me, etc.

The thing is, he often meows at the door like he's genuinely hurt and I can't stand it, I want it to stop. I'm thinking about just letting him go, even if I live in a big city. Could that be that bad of an idea? Or could there be another way to distract him from going outside?