As PLeblond mentions, there are requirements to actually fly a “real” plane, under supervision, after simulator qualification, but it does happen IRL on active flights. I was actually riding a jump seat for a First Officer undergoing his IOE training on a MD-80, which tells you it was circa 25 years ago, and even then the sims were considered sufficiently realistic. This was the First Officer having his first flight behind actual real life controls in an MD-80, and the Captain was very experienced and a rated instructor on the aircraft. The FO had literally hundreds of hours on various MD-80 simulators and system emulators, and did just fine. The plan was a three-day flight line, comprising a dozen or so legs. As I recall, the FO was coming into the role from a position as a Captain flying turboprops for a regional carrier.