The Move Shop.
While Pokémon Legends: Arceus lacks TMs and Egg Moves, it does have a new form of getting moves. At the Training Grounds, Zisu will provide you with many services, one of which is to teach your Pokémon some new moves in exchange for money.
These moves are added to as you progress through the game's story and for many Pokémon are the only way to get the moves on the Pokémon.
As Pokémon don't learn them on level up, they cannot be Mastered normally so require you to get a Seed of Mastery to give to Zisu in order to unlock their Agile and Strong Styles.
Hope I helped!
Serebii’s page on the Move Shop
