With a successful 0°F (-17°C) flight, I'll try -10°F (-23°C) next.I've kept it at -10°C or above this winter at ground level. I'm sure it's colder than that in the sky. No issues. I keep my batteries warm before I fly. On the few days it was colder than that, I kept it grounded.
The key is starting the flight with a warm drone battery [ 77°F (25°C) ] and monitoring the battery temperature and voltages VERY carefully in-flight.
It can be done safely for those reading!