Complete the Sinnoh Pokedex
Those who want their Pokemon journey to continue will be happy to know that the game doesn’t end after beating the Champion. The “gotta catch ’em all” slogan isn’t just for show here, since completing the Sinnoh Pokedex will actually open up a ton of new content, including areas that didn’t exist in the original Gen IV games.
There are 150 Pokemon to catch (plus a gifted Manaphy to redeem) to fill Sinnoh’s Pokedex. After going through all that trouble, you can speak to Professor Rowan in Sandgem Town to obtain the National Dex, which increases the grand total to 493 possible entries to catch.
Filling up the National Dex should keep you busy for a good amount of time, especially since Pokemon Home isn’t yet compatible with Brilliant Diamond and Shining Pearl. Time to add those entries the old-fashioned way.