Ideas
Prom is not on the calendar for my sims, and I have not been able to get it to be there despite trying to turn off aging, and switching normal lifespan to long lifespan. I also have the 'allow romantic and friendly interactions' button on, and have repaired the game. Not really sure what else to do, a few other sims asked to go come over to my sim's house for a pre-prom party but then prom never happened afterwards. I have gotten no prom interactions since, I don't have the option to ask anyone or make a sign, I even tried going to the auditorium the day of prom to try to trigger the event but nothing happened.
I have the same issue. Only way prom works is to open an old save-file from years ago. Creating a new one doesn’t work. I also tried re-installing HSY, didn’t help either. It’s like prom is deleted from the game like someone else here said. So annoying!!