Accidents in apartment common areas while potty training

Hi all, currently still working on potty training my 6 month old puppy. When he was younger we’d always carry him from our apartment, through the long hallway, down the elevator, and outdoors to a specific area to potty at. With this method he’s been pretty good, but the problem lately has been that if he isn’t carried it’s 50/50 if he will have an accident, usually in the elevator or hallway on the way out. I’ve noticed it’s after usually naps that he cannot hold it.

Any recommendations or tips for those who live in apartments? He’s only 15lbs so it’s no problem to carry him, but at some point I’d like him to be able to walk on his own without an accident. When did you know it was ok to have your dog walk down for bathrooms instead of carry. Thanks in advance!