We cruised on the Grand Princess in the Mexican Baja peninsula for 10 days at the start of March.
The pre-embarkation process was grim. The medallion app is horrid to use and is/was required to enter the required information to be ready for embarkation. It took hours, it didn’t recognize our address and as a result we couldn’t put in return airports etc. Two calls to customer service were required to get the issues resolved (somewhat), at least as far as was needed to get into the “green lane” to be able to book a time for embarking the ship. The app is a major PITA, and needs to be fixed.
We flew to LA the day before and stayed near the port overnight. Strategically this let us use one Covid antigen test for both our flight to the US (1 day prior) and getting on the cruise (2 days before). We also used Princess Air, and the flights were excellent.