I learnt English as a kid with the 12h time, but UK friends nowadays say they tend to use 24h everywhere precision is needed (e.g. transport timetables) and less and less 12h in everyday chat.
I was supposing USA was the same. Obviously not.
That is the direct opposite of my personal experience.
I do not live in the UK; I live in the Isle of Man, nearby. I visit for work often, though. Yes, the 24h clock is used for things like transport times, but in daily life, written and spoken, it is basically always 12h. I would estimate 95-99% of the time.