Persona 5 Royal will be coming in with a few new contents including the third new semester which will come with a new palace.
This new content will start off after the events of the main game so you will need to hit a certain requirement before you jump in. To start things off, players will need to rank up to three separate Confidants to a certain rank before the dates and some ranks are gated by certain days and events so you will need to hit so that you do not miss out on any extra gameplay.
You will also need to make sure that the Persona that you carry is with the same arcana as the person you are hanging out with to get more points, dialogue options and rank up faster. You also need to make sure you refuse any deals that would compromise your morals through the course of the story.
Following these steps will ensure you get all the new content has to offer.