One thing that has not been mentioned is immediately when you board the ship go to deck 4 in front of the Attic (Comedy/Nightclub venue).... or upon stepping into the Promenade immediately ask a staff member where the Show reservation desk is. Normally there is a desk there with RCL staff adding show reservations for cruisers for the whole week. Also, if you are tech savvy and know the RCL app, those same shows will be available from the app the day you board.
I've recently been on both Symphony and Harmony (Jan & April 2023) within 3 weeks last minute booking, with all shows showing "sold out" on the cruise planner, and yet I had reservation to ALL shows the day I boarded. Not only that, I attended Columbus twice, Grease twice, the water show twice... standby line was no problem finding seats within 15 min of the show starting. By the way, I only had a very late boarding check in time (2-2:30pm) because of my very late booking of the cruise, and still got all shows reserved once on board without a single issue even though most of the ship had already boarded before me.
@jlewisrnBreathe ... relax