No train ticket, just passport? For real? 🤯

Hi, I am heading to HK, GZ, Guilin and Yunnan in mid October with my wife. Going to be catching trains to get around. I haven't been for 6 years but I just heard that these days if you pre-book train tickets on Trip.com then you just show your passport at the station to board the train, no need to line up at those crazy ticket counter lines to collect physical tickets like it used to be 6 years ago! Is this true??? Thanks!